diff --git a/src/async-components/views/dialogs/eventindex/ManageEventIndexDialog.tsx b/src/async-components/views/dialogs/eventindex/ManageEventIndexDialog.tsx
index 1022bf5ff2..517a56d23b 100644
--- a/src/async-components/views/dialogs/eventindex/ManageEventIndexDialog.tsx
+++ b/src/async-components/views/dialogs/eventindex/ManageEventIndexDialog.tsx
@@ -38,7 +38,7 @@ interface IState {
     eventCount: number;
     crawlingRoomsCount: number;
     roomCount: number;
-    currentRoom: string;
+    currentRoom: string | null;
     crawlerSleepTime: number;
 }
 
@@ -61,7 +61,8 @@ export default class ManageEventIndexDialog extends React.Component<IProps, ISta
 
     public updateCurrentRoom = async (room: Room): Promise<void> => {
         const eventIndex = EventIndexPeg.get();
-        let stats: IIndexStats;
+        if (!eventIndex) return;
+        let stats: IIndexStats | undefined;
 
         try {
             stats = await eventIndex.getStats();
@@ -71,7 +72,7 @@ export default class ManageEventIndexDialog extends React.Component<IProps, ISta
             return;
         }
 
-        let currentRoom = null;
+        let currentRoom: string | null = null;
 
         if (room) currentRoom = room.name;
         const roomStats = eventIndex.crawlingRooms();
@@ -79,8 +80,8 @@ export default class ManageEventIndexDialog extends React.Component<IProps, ISta
         const roomCount = roomStats.totalRooms.size;
 
         this.setState({
-            eventIndexSize: stats.size,
-            eventCount: stats.eventCount,
+            eventIndexSize: stats?.size ?? 0,
+            eventCount: stats?.eventCount ?? 0,
             crawlingRoomsCount: crawlingRoomsCount,
             roomCount: roomCount,
             currentRoom: currentRoom,
@@ -100,7 +101,7 @@ export default class ManageEventIndexDialog extends React.Component<IProps, ISta
         let crawlingRoomsCount = 0;
         let roomCount = 0;
         let eventCount = 0;
-        let currentRoom = null;
+        let currentRoom: string | null = null;
 
         const eventIndex = EventIndexPeg.get();
 
@@ -109,8 +110,10 @@ export default class ManageEventIndexDialog extends React.Component<IProps, ISta
 
             try {
                 const stats = await eventIndex.getStats();
-                eventIndexSize = stats.size;
-                eventCount = stats.eventCount;
+                if (stats) {
+                    eventIndexSize = stats.size;
+                    eventCount = stats.eventCount;
+                }
             } catch {
                 // This call may fail if sporadically, not a huge issue as we
                 // will try later again in the updateCurrentRoom call and
@@ -136,7 +139,7 @@ export default class ManageEventIndexDialog extends React.Component<IProps, ISta
 
     private onDisable = async (): Promise<void> => {
         const DisableEventIndexDialog = (await import("./DisableEventIndexDialog")).default;
-        Modal.createDialog(DisableEventIndexDialog, null, null, /* priority = */ false, /* static = */ true);
+        Modal.createDialog(DisableEventIndexDialog, undefined, undefined, /* priority = */ false, /* static = */ true);
     };
 
     private onCrawlerSleepTimeChange = (e: ChangeEvent<HTMLInputElement>): void => {
diff --git a/src/async-components/views/dialogs/security/CreateKeyBackupDialog.tsx b/src/async-components/views/dialogs/security/CreateKeyBackupDialog.tsx
index 1669dd3c14..ec8cf31f30 100644
--- a/src/async-components/views/dialogs/security/CreateKeyBackupDialog.tsx
+++ b/src/async-components/views/dialogs/security/CreateKeyBackupDialog.tsx
@@ -49,7 +49,7 @@ interface IProps {
 }
 
 interface IState {
-    secureSecretStorage: boolean;
+    secureSecretStorage: boolean | null;
     phase: Phase;
     passPhrase: string;
     passPhraseValid: boolean;
@@ -121,7 +121,7 @@ export default class CreateKeyBackupDialog extends React.PureComponent<IProps, I
         const { secureSecretStorage } = this.state;
         this.setState({
             phase: Phase.BackingUp,
-            error: null,
+            error: undefined,
         });
         let info;
         try {
@@ -219,7 +219,7 @@ export default class CreateKeyBackupDialog extends React.PureComponent<IProps, I
 
     private onPassPhraseValidate = (result: IValidationResult): void => {
         this.setState({
-            passPhraseValid: result.valid,
+            passPhraseValid: !!result.valid,
         });
     };
 
@@ -306,7 +306,7 @@ export default class CreateKeyBackupDialog extends React.PureComponent<IProps, I
             changeText = _t("Go back to set it again.");
         }
 
-        let passPhraseMatch = null;
+        let passPhraseMatch: JSX.Element | undefined;
         if (matchText) {
             passPhraseMatch = (
                 <div className="mx_CreateKeyBackupDialog_passPhraseMatch">
diff --git a/src/async-components/views/dialogs/security/CreateSecretStorageDialog.tsx b/src/async-components/views/dialogs/security/CreateSecretStorageDialog.tsx
index 36ebf3ad8a..3e48739826 100644
--- a/src/async-components/views/dialogs/security/CreateSecretStorageDialog.tsx
+++ b/src/async-components/views/dialogs/security/CreateSecretStorageDialog.tsx
@@ -81,13 +81,13 @@ interface IState {
     copied: boolean;
     downloaded: boolean;
     setPassphrase: boolean;
-    backupInfo: IKeyBackupInfo;
-    backupSigStatus: TrustInfo;
+    backupInfo: IKeyBackupInfo | null;
+    backupSigStatus: TrustInfo | null;
     // does the server offer a UI auth flow with just m.login.password
     // for /keys/device_signing/upload?
-    canUploadKeysWithPasswordOnly: boolean;
+    canUploadKeysWithPasswordOnly: boolean | null;
     accountPassword: string;
-    accountPasswordCorrect: boolean;
+    accountPasswordCorrect: boolean | null;
     canSkip: boolean;
     passPhraseKeySelected: string;
     error?: string;
@@ -119,7 +119,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
         }
 
         const accountPassword = props.accountPassword || "";
-        let canUploadKeysWithPasswordOnly = null;
+        let canUploadKeysWithPasswordOnly: boolean | null = null;
         if (accountPassword) {
             // If we have an account password in memory, let's simplify and
             // assume it means password auth is also supported for device
@@ -172,12 +172,14 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
         this.fetchBackupInfo();
     }
 
-    private async fetchBackupInfo(): Promise<{ backupInfo: IKeyBackupInfo; backupSigStatus: TrustInfo }> {
+    private async fetchBackupInfo(): Promise<{ backupInfo?: IKeyBackupInfo; backupSigStatus?: TrustInfo }> {
         try {
             const backupInfo = await MatrixClientPeg.get().getKeyBackupVersion();
             const backupSigStatus =
                 // we may not have started crypto yet, in which case we definitely don't trust the backup
-                MatrixClientPeg.get().isCryptoEnabled() && (await MatrixClientPeg.get().isKeyBackupTrusted(backupInfo));
+                backupInfo && MatrixClientPeg.get().isCryptoEnabled()
+                    ? await MatrixClientPeg.get().isKeyBackupTrusted(backupInfo)
+                    : null;
 
             const { forceReset } = this.props;
             const phase = backupInfo && !forceReset ? Phase.Migrate : Phase.ChooseKeyPassphrase;
@@ -189,17 +191,18 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
             });
 
             return {
-                backupInfo,
-                backupSigStatus,
+                backupInfo: backupInfo ?? undefined,
+                backupSigStatus: backupSigStatus ?? undefined,
             };
         } catch (e) {
             this.setState({ phase: Phase.LoadError });
+            return {};
         }
     }
 
     private async queryKeyUploadAuth(): Promise<void> {
         try {
-            await MatrixClientPeg.get().uploadDeviceSigningKeys(null, {} as CrossSigningKeys);
+            await MatrixClientPeg.get().uploadDeviceSigningKeys(undefined, {} as CrossSigningKeys);
             // We should never get here: the server should always require
             // UI auth to upload device signing keys. If we do, we upload
             // no keys which would be a no-op.
@@ -248,7 +251,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
 
     private onMigrateFormSubmit = (e: React.FormEvent): void => {
         e.preventDefault();
-        if (this.state.backupSigStatus.usable) {
+        if (this.state.backupSigStatus?.usable) {
             this.bootstrapSecretStorage();
         } else {
             this.restoreBackup();
@@ -265,7 +268,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
     };
 
     private onDownloadClick = (): void => {
-        const blob = new Blob([this.recoveryKey.encodedPrivateKey], {
+        const blob = new Blob([this.recoveryKey.encodedPrivateKey!], {
             type: "text/plain;charset=us-ascii",
         });
         FileSaver.saveAs(blob, "security-key.txt");
@@ -323,7 +326,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
     private bootstrapSecretStorage = async (): Promise<void> => {
         this.setState({
             phase: Phase.Storing,
-            error: null,
+            error: undefined,
         });
 
         const cli = MatrixClientPeg.get();
@@ -351,7 +354,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
                 });
                 await cli.bootstrapSecretStorage({
                     createSecretStorageKey: async () => this.recoveryKey,
-                    keyBackupInfo: this.state.backupInfo,
+                    keyBackupInfo: this.state.backupInfo!,
                     setupNewKeyBackup: !this.state.backupInfo,
                     getKeyBackupPassphrase: async (): Promise<Uint8Array> => {
                         // We may already have the backup key if we earlier went
@@ -399,14 +402,14 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
                 showSummary: false,
                 keyCallback,
             },
-            null,
+            undefined,
             /* priority = */ false,
             /* static = */ false,
         );
 
         await finished;
         const { backupSigStatus } = await this.fetchBackupInfo();
-        if (backupSigStatus.usable && this.state.canUploadKeysWithPasswordOnly && this.state.accountPassword) {
+        if (backupSigStatus?.usable && this.state.canUploadKeysWithPasswordOnly && this.state.accountPassword) {
             this.bootstrapSecretStorage();
         }
     };
@@ -467,7 +470,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
 
     private onPassPhraseValidate = (result: IValidationResult): void => {
         this.setState({
-            passPhraseValid: result.valid,
+            passPhraseValid: !!result.valid,
         });
     };
 
@@ -581,13 +584,13 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
                             label={_t("Password")}
                             value={this.state.accountPassword}
                             onChange={this.onAccountPasswordChange}
-                            forceValidity={this.state.accountPasswordCorrect === false ? false : null}
+                            forceValidity={this.state.accountPasswordCorrect === false ? false : undefined}
                             autoFocus={true}
                         />
                     </div>
                 </div>
             );
-        } else if (!this.state.backupSigStatus.usable) {
+        } else if (!this.state.backupSigStatus?.usable) {
             authPrompt = (
                 <div>
                     <div>{_t("Restore your key backup to upgrade your encryption")}</div>
@@ -612,7 +615,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
                     primaryButton={nextCaption}
                     onPrimaryButtonClick={this.onMigrateFormSubmit}
                     hasCancel={false}
-                    primaryDisabled={this.state.canUploadKeysWithPasswordOnly && !this.state.accountPassword}
+                    primaryDisabled={!!this.state.canUploadKeysWithPasswordOnly && !this.state.accountPassword}
                 >
                     <button type="button" className="danger" onClick={this.onCancelClick}>
                         {_t("Skip")}
@@ -680,7 +683,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
             changeText = _t("Go back to set it again.");
         }
 
-        let passPhraseMatch = null;
+        let passPhraseMatch: JSX.Element | undefined;
         if (matchText) {
             passPhraseMatch = (
                 <div>
@@ -721,7 +724,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
     }
 
     private renderPhaseShowKey(): JSX.Element {
-        let continueButton;
+        let continueButton: JSX.Element;
         if (this.state.phase === Phase.ShowKey) {
             continueButton = (
                 <DialogButtons
@@ -928,7 +931,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
             }
         }
 
-        let titleClass = null;
+        let titleClass: string | string[] | undefined;
         switch (this.state.phase) {
             case Phase.Passphrase:
             case Phase.PassphraseConfirm:
diff --git a/src/async-components/views/dialogs/security/ExportE2eKeysDialog.tsx b/src/async-components/views/dialogs/security/ExportE2eKeysDialog.tsx
index 518f985dd8..139ede4d9c 100644
--- a/src/async-components/views/dialogs/security/ExportE2eKeysDialog.tsx
+++ b/src/async-components/views/dialogs/security/ExportE2eKeysDialog.tsx
@@ -38,7 +38,7 @@ interface IProps {
 
 interface IState {
     phase: Phase;
-    errStr: string;
+    errStr: string | null;
     passphrase1: string;
     passphrase2: string;
 }
diff --git a/src/async-components/views/dialogs/security/ImportE2eKeysDialog.tsx b/src/async-components/views/dialogs/security/ImportE2eKeysDialog.tsx
index f6d488716c..d2552b4093 100644
--- a/src/async-components/views/dialogs/security/ImportE2eKeysDialog.tsx
+++ b/src/async-components/views/dialogs/security/ImportE2eKeysDialog.tsx
@@ -28,7 +28,11 @@ function readFileAsArrayBuffer(file: File): Promise<ArrayBuffer> {
     return new Promise((resolve, reject) => {
         const reader = new FileReader();
         reader.onload = (e) => {
-            resolve(e.target.result as ArrayBuffer);
+            if (e.target?.result) {
+                resolve(e.target.result as ArrayBuffer);
+            } else {
+                reject(new Error("Failed to read file due to unknown error"));
+            }
         };
         reader.onerror = reject;
 
@@ -49,7 +53,7 @@ interface IProps {
 interface IState {
     enableSubmit: boolean;
     phase: Phase;
-    errStr: string;
+    errStr: string | null;
     passphrase: string;
 }
 
@@ -73,7 +77,7 @@ export default class ImportE2eKeysDialog extends React.Component<IProps, IState>
     }
 
     private onFormChange = (): void => {
-        const files = this.file.current.files;
+        const files = this.file.current?.files;
         this.setState({
             enableSubmit: this.state.passphrase !== "" && !!files?.length,
         });
@@ -87,7 +91,10 @@ export default class ImportE2eKeysDialog extends React.Component<IProps, IState>
     private onFormSubmit = (ev: React.FormEvent): boolean => {
         ev.preventDefault();
         // noinspection JSIgnoredPromiseFromCall
-        this.startImport(this.file.current.files[0], this.state.passphrase);
+        const file = this.file.current?.files?.[0];
+        if (file) {
+            this.startImport(file, this.state.passphrase);
+        }
         return false;
     };
 
diff --git a/src/async-components/views/dialogs/security/RecoveryMethodRemovedDialog.tsx b/src/async-components/views/dialogs/security/RecoveryMethodRemovedDialog.tsx
index cb318e61fb..7363f192a2 100644
--- a/src/async-components/views/dialogs/security/RecoveryMethodRemovedDialog.tsx
+++ b/src/async-components/views/dialogs/security/RecoveryMethodRemovedDialog.tsx
@@ -39,7 +39,7 @@ export default class RecoveryMethodRemovedDialog extends React.PureComponent<IPr
         Modal.createDialogAsync(
             import("./CreateKeyBackupDialog") as unknown as Promise<ComponentType<{}>>,
             undefined,
-            null,
+            undefined,
             /* priority = */ false,
             /* static = */ true,
         );
diff --git a/src/utils/strings.ts b/src/utils/strings.ts
index 23ea37ed28..d065339f1f 100644
--- a/src/utils/strings.ts
+++ b/src/utils/strings.ts
@@ -70,7 +70,8 @@ export function selectText(target: Element): void {
  * In certain browsers it may only work if triggered by a user action or may ask user for permissions
  * @param ref pointer to the node to copy
  */
-export function copyNode(ref: Element): boolean {
+export function copyNode(ref?: Element | null): boolean {
+    if (!ref) return false;
     selectText(ref);
     return document.execCommand("copy");
 }