strictNullChecks (#4666)

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src/mfm/fromHtml.ts

@@ -3,8 +3,6 @@ import { URL } from 'url';
 import { urlRegex } from './prelude';
 
 export function fromHtml(html: string): string {
-	if (html == null) return null;
-
 	const dom = parseFragment(html) as DefaultTreeDocumentFragment;
 
 	let text = '';

src/mfm/parse.ts

@@ -2,7 +2,7 @@ import { mfmLanguage } from './language';
 import { MfmForest } from './prelude';
 import { normalize } from './normalize';
 
-export function parse(source: string): MfmForest {
+export function parse(source: string | null): MfmForest | null {
 	if (source == null || source == '') {
 		return null;
 	}
@@ -10,7 +10,7 @@ export function parse(source: string): MfmForest {
 	return normalize(mfmLanguage.root.tryParse(source));
 }
 
-export function parsePlain(source: string): MfmForest {
+export function parsePlain(source: string | null): MfmForest | null {
 	if (source == null || source == '') {
 		return null;
 	}

src/mfm/toHtml.ts

@@ -4,7 +4,7 @@ import { intersperse } from '../prelude/array';
 import { MfmForest, MfmTree } from './prelude';
 import { IMentionedRemoteUsers } from '../models/entities/note';
 
-export function toHtml(tokens: MfmForest, mentionedRemoteUsers: IMentionedRemoteUsers = []) {
+export function toHtml(tokens: MfmForest | null, mentionedRemoteUsers: IMentionedRemoteUsers = []) {
 	if (tokens == null) {
 		return null;
 	}