diff --git a/src/components/views/rooms/BasicMessageComposer.tsx b/src/components/views/rooms/BasicMessageComposer.tsx
index d6cfb3038a..e7bb866ec0 100644
--- a/src/components/views/rooms/BasicMessageComposer.tsx
+++ b/src/components/views/rooms/BasicMessageComposer.tsx
@@ -573,24 +573,28 @@ export default class BasicMessageEditor extends React.Component<IProps, IState>
                 this.onFormatAction(Formatting.InsertLink);
                 handled = true;
                 break;
-            case KeyBindingAction.EditRedo:
-                if (this.historyManager.canRedo()) {
-                    const { parts, caret } = this.historyManager.redo();
+            case KeyBindingAction.EditRedo: {
+                const history = this.historyManager.redo();
+                if (history) {
+                    const { parts, caret } = history;
                     // pass matching inputType so historyManager doesn't push echo
                     // when invoked from rerender callback.
                     model.reset(parts, caret, "historyRedo");
                 }
                 handled = true;
                 break;
-            case KeyBindingAction.EditUndo:
-                if (this.historyManager.canUndo()) {
-                    const { parts, caret } = this.historyManager.undo(this.props.model);
+            }
+            case KeyBindingAction.EditUndo: {
+                const history = this.historyManager.undo(this.props.model);
+                if (history) {
+                    const { parts, caret } = history;
                     // pass matching inputType so historyManager doesn't push echo
                     // when invoked from rerender callback.
                     model.reset(parts, caret, "historyUndo");
                 }
                 handled = true;
                 break;
+            }
             case KeyBindingAction.NewLine:
                 this.insertText("\n");
                 handled = true;
diff --git a/src/editor/autocomplete.ts b/src/editor/autocomplete.ts
index 8bde9ee23d..199b43a26f 100644
--- a/src/editor/autocomplete.ts
+++ b/src/editor/autocomplete.ts
@@ -99,12 +99,15 @@ export default class AutocompleteWrapperModel {
         const text = completion.completion;
         switch (completion.type) {
             case "room":
-                return [this.partCreator.roomPill(text, completionId), this.partCreator.plain(completion.suffix)];
+                return [this.partCreator.roomPill(text, completionId), this.partCreator.plain(completion.suffix || "")];
             case "at-room":
-                return [this.partCreator.atRoomPill(completionId), this.partCreator.plain(completion.suffix)];
+                return [
+                    this.partCreator.atRoomPill(completionId || ""),
+                    this.partCreator.plain(completion.suffix || ""),
+                ];
             case "user":
                 // Insert suffix only if the pill is the part with index 0 - we are at the start of the composer
-                return this.partCreator.createMentionParts(this.partIndex === 0, text, completionId);
+                return this.partCreator.createMentionParts(this.partIndex === 0, text, completionId || "");
             case "command":
                 // command needs special handling for auto complete, but also renders as plain texts
                 return [(this.partCreator as CommandPartCreator).command(text)];
diff --git a/src/editor/commands.tsx b/src/editor/commands.tsx
index 71f9b678b3..88db48a899 100644
--- a/src/editor/commands.tsx
+++ b/src/editor/commands.tsx
@@ -137,5 +137,5 @@ export async function shouldSendAnyway(commandText: string): Promise<boolean> {
         button: _t("Send as message"),
     });
     const [sendAnyway] = await finished;
-    return sendAnyway;
+    return sendAnyway || false;
 }
diff --git a/src/editor/deserialize.ts b/src/editor/deserialize.ts
index 0c57ff4b0c..d39199f124 100644
--- a/src/editor/deserialize.ts
+++ b/src/editor/deserialize.ts
@@ -78,7 +78,7 @@ function parseLink(n: Node, pc: PartCreator, opts: IParseOptions): Part[] {
 
     switch (resourceId?.[0]) {
         case "@":
-            return [pc.userPill(n.textContent, resourceId)];
+            return [pc.userPill(n.textContent || "", resourceId)];
         case "#":
             return [pc.roomPill(resourceId)];
     }
@@ -97,6 +97,8 @@ function parseImage(n: Node, pc: PartCreator, opts: IParseOptions): Part[] {
 }
 
 function parseCodeBlock(n: Node, pc: PartCreator, opts: IParseOptions): Part[] {
+    if (!n.textContent) return [];
+
     let language = "";
     if (n.firstChild?.nodeName === "CODE") {
         for (const className of (n.firstChild as HTMLElement).classList) {
@@ -170,7 +172,7 @@ function parseNode(n: Node, pc: PartCreator, opts: IParseOptions, mkListItem?: (
 
     switch (n.nodeType) {
         case Node.TEXT_NODE:
-            return parseAtRoomMentions(n.nodeValue, pc, opts);
+            return parseAtRoomMentions(n.nodeValue || "", pc, opts);
         case Node.ELEMENT_NODE:
             switch (n.nodeName) {
                 case "H1":
@@ -204,7 +206,7 @@ function parseNode(n: Node, pc: PartCreator, opts: IParseOptions, mkListItem?: (
                     return parseCodeBlock(n, pc, opts);
                 case "CODE": {
                     // Escape backticks by using multiple backticks for the fence if necessary
-                    const fence = "`".repeat(longestBacktickSequence(n.textContent) + 1);
+                    const fence = "`".repeat(longestBacktickSequence(n.textContent || "") + 1);
                     return pc.plainWithEmoji(`${fence}${n.textContent}${fence}`);
                 }
                 case "BLOCKQUOTE": {
diff --git a/src/editor/dom.ts b/src/editor/dom.ts
index 05d5789066..7c3fd3072b 100644
--- a/src/editor/dom.ts
+++ b/src/editor/dom.ts
@@ -34,11 +34,11 @@ export function walkDOMDepthFirst(rootNode: Node, enterNodeCallback: Predicate,
         } else {
             while (node && !node.nextSibling && node !== rootNode) {
                 node = node.parentElement;
-                if (node !== rootNode) {
+                if (node && node !== rootNode) {
                     leaveNodeCallback(node);
                 }
             }
-            if (node !== rootNode) {
+            if (node && node !== rootNode) {
                 node = node.nextSibling;
             }
         }
@@ -57,10 +57,10 @@ export function getCaretOffsetAndText(
 }
 
 function tryReduceSelectionToTextNode(
-    selectionNode: Node,
+    selectionNode: Node | null,
     selectionOffset: number,
 ): {
-    node: Node;
+    node: Node | null;
     characterOffset: number;
 } {
     // if selectionNode is an element, the selected location comes after the selectionOffset-th child node,
@@ -73,8 +73,8 @@ function tryReduceSelectionToTextNode(
         if (childNodeCount) {
             if (selectionOffset >= childNodeCount) {
                 selectionNode = selectionNode.lastChild;
-                if (selectionNode.nodeType === Node.TEXT_NODE) {
-                    selectionOffset = selectionNode.textContent.length;
+                if (selectionNode?.nodeType === Node.TEXT_NODE) {
+                    selectionOffset = selectionNode.textContent?.length || 0;
                 } else {
                     // this will select the last child node in the next iteration
                     selectionOffset = Number.MAX_SAFE_INTEGER;
@@ -101,7 +101,7 @@ function tryReduceSelectionToTextNode(
 
 function getSelectionOffsetAndText(
     editor: HTMLDivElement,
-    selectionNode: Node,
+    selectionNode: Node | null,
     selectionOffset: number,
 ): {
     offset: DocumentOffset;
@@ -115,14 +115,15 @@ function getSelectionOffsetAndText(
 
 // gets the caret position details, ignoring and adjusting to
 // the ZWS if you're typing in a caret node
-function getCaret(node: Node, offsetToNode: number, offsetWithinNode: number): DocumentOffset {
+function getCaret(node: Node | null, offsetToNode: number, offsetWithinNode: number): DocumentOffset {
     // if no node is selected, return an offset at the start
     if (!node) {
         return new DocumentOffset(0, false);
     }
-    let atNodeEnd = offsetWithinNode === node.textContent.length;
+    let atNodeEnd = offsetWithinNode === node.textContent?.length;
     if (node.nodeType === Node.TEXT_NODE && isCaretNode(node.parentElement)) {
-        const zwsIdx = node.nodeValue.indexOf(CARET_NODE_CHAR);
+        const nodeValue = node.nodeValue || "";
+        const zwsIdx = nodeValue.indexOf(CARET_NODE_CHAR);
         if (zwsIdx !== -1 && zwsIdx < offsetWithinNode) {
             offsetWithinNode -= 1;
         }
@@ -138,7 +139,10 @@ function getCaret(node: Node, offsetToNode: number, offsetWithinNode: number): D
 // gets the text of the editor as a string,
 // and the offset in characters where the selectionNode starts in that string
 // all ZWS from caret nodes are filtered out
-function getTextAndOffsetToNode(editor: HTMLDivElement, selectionNode: Node): { offsetToNode: number; text: string } {
+function getTextAndOffsetToNode(
+    editor: HTMLDivElement,
+    selectionNode: Node | null,
+): { offsetToNode: number; text: string } {
     let offsetToNode = 0;
     let foundNode = false;
     let text = "";
diff --git a/src/editor/history.ts b/src/editor/history.ts
index 351d9709ec..074c65cf10 100644
--- a/src/editor/history.ts
+++ b/src/editor/history.ts
@@ -19,7 +19,7 @@ import { IDiff } from "./diff";
 import { SerializedPart } from "./parts";
 import { Caret } from "./caret";
 
-interface IHistory {
+export interface IHistory {
     parts: SerializedPart[];
     caret: Caret;
 }
@@ -121,7 +121,7 @@ export default class HistoryManager {
     }
 
     public ensureLastChangesPushed(model: EditorModel): void {
-        if (this.changedSinceLastPush) {
+        if (this.changedSinceLastPush && this.lastCaret) {
             this.pushState(model, this.lastCaret);
         }
     }
@@ -135,7 +135,7 @@ export default class HistoryManager {
     }
 
     // returns state that should be applied to model
-    public undo(model: EditorModel): IHistory {
+    public undo(model: EditorModel): IHistory | void {
         if (this.canUndo()) {
             this.ensureLastChangesPushed(model);
             this.currentIndex -= 1;
@@ -144,7 +144,7 @@ export default class HistoryManager {
     }
 
     // returns state that should be applied to model
-    public redo(): IHistory {
+    public redo(): IHistory | void {
         if (this.canRedo()) {
             this.changedSinceLastPush = false;
             this.currentIndex += 1;
diff --git a/src/editor/model.ts b/src/editor/model.ts
index 2e30442e02..8463540ebb 100644
--- a/src/editor/model.ts
+++ b/src/editor/model.ts
@@ -91,16 +91,18 @@ export default class EditorModel {
     }
 
     public clone(): EditorModel {
-        const clonedParts = this.parts.map((p) => this.partCreator.deserializePart(p.serialize()));
+        const clonedParts = this.parts
+            .map((p) => this.partCreator.deserializePart(p.serialize()))
+            .filter((p): p is Part => Boolean(p));
         return new EditorModel(clonedParts, this._partCreator, this.updateCallback);
     }
 
     private insertPart(index: number, part: Part): void {
         this._parts.splice(index, 0, part);
-        if (this.activePartIdx >= index) {
+        if (this.activePartIdx && this.activePartIdx >= index) {
             ++this.activePartIdx;
         }
-        if (this.autoCompletePartIdx >= index) {
+        if (this.autoCompletePartIdx && this.autoCompletePartIdx >= index) {
             ++this.autoCompletePartIdx;
         }
     }
@@ -109,12 +111,12 @@ export default class EditorModel {
         this._parts.splice(index, 1);
         if (index === this.activePartIdx) {
             this.activePartIdx = null;
-        } else if (this.activePartIdx > index) {
+        } else if (this.activePartIdx && this.activePartIdx > index) {
             --this.activePartIdx;
         }
         if (index === this.autoCompletePartIdx) {
             this.autoCompletePartIdx = null;
-        } else if (this.autoCompletePartIdx > index) {
+        } else if (this.autoCompletePartIdx && this.autoCompletePartIdx > index) {
             --this.autoCompletePartIdx;
         }
     }
@@ -160,7 +162,9 @@ export default class EditorModel {
     }
 
     public reset(serializedParts: SerializedPart[], caret?: Caret, inputType?: string): void {
-        this._parts = serializedParts.map((p) => this._partCreator.deserializePart(p));
+        this._parts = serializedParts
+            .map((p) => this._partCreator.deserializePart(p))
+            .filter((p): p is Part => Boolean(p));
         if (!caret) {
             caret = this.getPositionAtEnd();
         }
@@ -194,7 +198,7 @@ export default class EditorModel {
 
     public update(newValue: string, inputType: string, caret: DocumentOffset): Promise<void> {
         const diff = this.diff(newValue, inputType, caret);
-        const position = this.positionForOffset(diff.at, caret.atNodeEnd);
+        const position = this.positionForOffset(diff.at || 0, caret.atNodeEnd);
         let removedOffsetDecrease = 0;
         if (diff.removed) {
             removedOffsetDecrease = this.removeText(position, diff.removed.length);
@@ -204,7 +208,7 @@ export default class EditorModel {
             addedLen = this.addText(position, diff.added, inputType);
         }
         this.mergeAdjacentParts();
-        const caretOffset = diff.at - removedOffsetDecrease + addedLen;
+        const caretOffset = (diff.at || 0) - removedOffsetDecrease + addedLen;
         let newPosition = this.positionForOffset(caretOffset, true);
         const canOpenAutoComplete = inputType !== "insertFromPaste" && inputType !== "insertFromDrop";
         const acPromise = this.setActivePart(newPosition, canOpenAutoComplete);
@@ -254,10 +258,11 @@ export default class EditorModel {
     private onAutoComplete = ({ replaceParts, close }: ICallback): void => {
         let pos: DocumentPosition | undefined;
         if (replaceParts) {
-            this._parts.splice(this.autoCompletePartIdx, this.autoCompletePartCount, ...replaceParts);
+            const autoCompletePartIdx = this.autoCompletePartIdx || 0;
+            this._parts.splice(autoCompletePartIdx, this.autoCompletePartCount, ...replaceParts);
             this.autoCompletePartCount = replaceParts.length;
             const lastPart = replaceParts[replaceParts.length - 1];
-            const lastPartIndex = this.autoCompletePartIdx + replaceParts.length - 1;
+            const lastPartIndex = autoCompletePartIdx + replaceParts.length - 1;
             pos = new DocumentPosition(lastPartIndex, lastPart.text.length);
         }
         if (close) {
@@ -360,10 +365,13 @@ export default class EditorModel {
         const { offset } = pos;
         let addLen = str.length;
         const part = this._parts[index];
+
+        let it: string | undefined = str;
+
         if (part) {
             if (part.canEdit) {
                 if (part.validateAndInsert(offset, str, inputType)) {
-                    str = null;
+                    it = undefined;
                 } else {
                     const splitPart = part.split(offset);
                     index += 1;
@@ -381,7 +389,6 @@ export default class EditorModel {
             index = 0;
         }
 
-        let it: string | undefined = str;
         while (it) {
             const newPart = this._partCreator.createPartForInput(it, index, inputType);
             const oldStr = it;
diff --git a/src/editor/operations.ts b/src/editor/operations.ts
index d7e4addd75..13db8d56aa 100644
--- a/src/editor/operations.ts
+++ b/src/editor/operations.ts
@@ -241,7 +241,7 @@ export function toggleInlineFormat(range: Range, prefix: string, suffix = prefix
     const { partCreator } = model;
 
     // compute paragraph [start, end] indexes
-    const paragraphIndexes = [];
+    const paragraphIndexes: [number, number][] = [];
     let startIndex = 0;
 
     // start at i=2 because we look at i and up to two parts behind to detect paragraph breaks at their end
@@ -285,12 +285,18 @@ export function toggleInlineFormat(range: Range, prefix: string, suffix = prefix
             // remove prefix and suffix formatting string
             const partWithoutPrefix = parts[base].serialize();
             partWithoutPrefix.text = partWithoutPrefix.text.slice(prefix.length);
-            parts[base] = partCreator.deserializePart(partWithoutPrefix);
+            let deserializedPart = partCreator.deserializePart(partWithoutPrefix);
+            if (deserializedPart) {
+                parts[base] = deserializedPart;
+            }
 
             const partWithoutSuffix = parts[index - 1].serialize();
             const suffixPartText = partWithoutSuffix.text;
             partWithoutSuffix.text = suffixPartText.substring(0, suffixPartText.length - suffix.length);
-            parts[index - 1] = partCreator.deserializePart(partWithoutSuffix);
+            deserializedPart = partCreator.deserializePart(partWithoutSuffix);
+            if (deserializedPart) {
+                parts[index - 1] = deserializedPart;
+            }
         } else {
             parts.splice(index, 0, partCreator.plain(suffix)); // splice in the later one first to not change offset
             parts.splice(base, 0, partCreator.plain(prefix));
diff --git a/src/editor/parts.ts b/src/editor/parts.ts
index 8fde5e4f84..271feadd39 100644
--- a/src/editor/parts.ts
+++ b/src/editor/parts.ts
@@ -76,7 +76,7 @@ interface IBasePart {
 
 interface IPillCandidatePart extends Omit<IBasePart, "type" | "createAutoComplete"> {
     type: Type.PillCandidate | Type.Command;
-    createAutoComplete(updateCallback: UpdateCallback): AutocompleteWrapperModel;
+    createAutoComplete(updateCallback: UpdateCallback): AutocompleteWrapperModel | undefined;
 }
 
 interface IPillPart extends Omit<IBasePart, "type" | "resourceId"> {
@@ -272,7 +272,7 @@ export abstract class PillPart extends BasePart implements IPillPart {
         const container = document.createElement("span");
         container.setAttribute("spellcheck", "false");
         container.setAttribute("contentEditable", "false");
-        container.onclick = this.onClick;
+        if (this.onClick) container.onclick = this.onClick;
         container.className = this.className;
         container.appendChild(document.createTextNode(this.text));
         this.setAvatar(container);
@@ -287,7 +287,7 @@ export abstract class PillPart extends BasePart implements IPillPart {
         if (node.className !== this.className) {
             node.className = this.className;
         }
-        if (node.onclick !== this.onClick) {
+        if (this.onClick && node.onclick !== this.onClick) {
             node.onclick = this.onClick;
         }
         this.setAvatar(node);
@@ -496,8 +496,8 @@ class PillCandidatePart extends PlainBasePart implements IPillCandidatePart {
         super(text);
     }
 
-    public createAutoComplete(updateCallback: UpdateCallback): AutocompleteWrapperModel {
-        return this.autoCompleteCreator.create(updateCallback);
+    public createAutoComplete(updateCallback: UpdateCallback): AutocompleteWrapperModel | undefined {
+        return this.autoCompleteCreator.create?.(updateCallback);
     }
 
     protected acceptsInsertion(chr: string, offset: number, inputType: string): boolean {
@@ -532,7 +532,7 @@ export function getAutoCompleteCreator(getAutocompleterComponent: GetAutocomplet
 type AutoCompleteCreator = ReturnType<typeof getAutoCompleteCreator>;
 
 interface IAutocompleteCreator {
-    create(updateCallback: UpdateCallback): AutocompleteWrapperModel;
+    create: ((updateCallback: UpdateCallback) => AutocompleteWrapperModel) | undefined;
 }
 
 export class PartCreator {
@@ -587,9 +587,9 @@ export class PartCreator {
             case Type.PillCandidate:
                 return this.pillCandidate(part.text);
             case Type.RoomPill:
-                return this.roomPill(part.resourceId);
+                return part.resourceId ? this.roomPill(part.resourceId) : undefined;
             case Type.UserPill:
-                return this.userPill(part.text, part.resourceId);
+                return part.resourceId ? this.userPill(part.text, part.resourceId) : undefined;
         }
     }
 
diff --git a/src/editor/range.ts b/src/editor/range.ts
index fcf19c0357..445185c375 100644
--- a/src/editor/range.ts
+++ b/src/editor/range.ts
@@ -118,7 +118,7 @@ export default class Range {
             const serializedPart = part.serialize();
             serializedPart.text = part.text.substring(startIdx, endIdx);
             const newPart = this.model.partCreator.deserializePart(serializedPart);
-            parts.push(newPart);
+            if (newPart) parts.push(newPart);
         });
         return parts;
     }
diff --git a/test/editor/history-test.ts b/test/editor/history-test.ts
index 25c2dca895..7436e8f588 100644
--- a/test/editor/history-test.ts
+++ b/test/editor/history-test.ts
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import HistoryManager, { MAX_STEP_LENGTH } from "../../src/editor/history";
+import HistoryManager, { IHistory, MAX_STEP_LENGTH } from "../../src/editor/history";
 import EditorModel from "../../src/editor/model";
 import DocumentPosition from "../../src/editor/position";
 
@@ -29,7 +29,7 @@ describe("editor/history", function () {
         parts[0] = "hello world";
         history.tryPush(model, new DocumentPosition(0, 0), "insertText", {});
         expect(history.canUndo()).toEqual(true);
-        const undoState = history.undo(model);
+        const undoState = history.undo(model) as IHistory;
         expect(undoState.caret).toBe(caret1);
         expect(undoState.parts).toEqual(["hello"]);
         expect(history.canUndo()).toEqual(false);
@@ -44,7 +44,7 @@ describe("editor/history", function () {
         history.tryPush(model, caret2, "insertText", {});
         history.undo(model);
         expect(history.canRedo()).toEqual(true);
-        const redoState = history.redo();
+        const redoState = history.redo() as IHistory;
         expect(redoState.caret).toBe(caret2);
         expect(redoState.parts).toEqual(["hello world"]);
         expect(history.canRedo()).toEqual(false);
@@ -74,7 +74,7 @@ describe("editor/history", function () {
             parts[0] = parts[0] + diff.added;
             keystrokeCount += 1;
         } while (!history.tryPush(model, new DocumentPosition(0, 0), "insertText", diff));
-        const undoState = history.undo(model);
+        const undoState = history.undo(model) as IHistory;
         expect(undoState.caret).toBe(firstCaret);
         expect(undoState.parts).toEqual(["hello"]);
         expect(history.canUndo()).toEqual(false);
@@ -104,7 +104,7 @@ describe("editor/history", function () {
         parts[0] = "hi you";
 
         expect(history.canUndo()).toEqual(true);
-        const undoResult = history.undo(model);
+        const undoResult = history.undo(model) as IHistory;
         expect(undoResult.caret).toEqual(spaceCaret);
         expect(undoResult.parts).toEqual(["hi "]);
     });
@@ -118,7 +118,7 @@ describe("editor/history", function () {
         const result = history.tryPush(model, new DocumentPosition(0, 0), "insertText", { added: "o" });
         expect(result).toEqual(false);
         expect(history.canUndo()).toEqual(true);
-        const undoState = history.undo(model);
+        const undoState = history.undo(model) as IHistory;
         expect(undoState.caret).toEqual(firstCaret);
         expect(undoState.parts).toEqual(["hello"]);
     });
@@ -132,7 +132,7 @@ describe("editor/history", function () {
         history.tryPush(model, caret, "insertText", { added: "o" });
         history.undo(model);
         expect(history.canRedo()).toEqual(true);
-        const redoState = history.redo();
+        const redoState = history.redo() as IHistory;
         expect(redoState.caret).toBe(caret);
         expect(redoState.parts).toEqual(["helloo"]);
     });