diff --git a/packages/backend/migration/1651224615271-foreign-key.js b/packages/backend/migration/1651224615271-foreign-key.js
new file mode 100644
index 000000000..44ba7fb6c
--- /dev/null
+++ b/packages/backend/migration/1651224615271-foreign-key.js
@@ -0,0 +1,89 @@
+export class foreignKeyReports1651224615271 {
+    name = 'foreignKeyReports1651224615271'
+
+    async up(queryRunner) {
+        await Promise.all([
+            queryRunner.query(`ALTER INDEX "public"."IDX_seoignmeoprigmkpodgrjmkpormg" RENAME TO "IDX_c8cc87bd0f2f4487d17c651fbf"`),
+            queryRunner.query(`DROP INDEX "public"."IDX_note_on_channelId_and_id_desc"`),
+
+            // remove unnecessary default null, see also down
+            queryRunner.query(`ALTER TABLE "user" ALTER COLUMN "followersUri" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "access_token" ALTER COLUMN "session" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "access_token" ALTER COLUMN "appId" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "access_token" ALTER COLUMN "name" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "access_token" ALTER COLUMN "description" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "access_token" ALTER COLUMN "iconUrl" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "instance" ALTER COLUMN "softwareName" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "instance" ALTER COLUMN "softwareVersion" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "instance" ALTER COLUMN "name" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "instance" ALTER COLUMN "description" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "instance" ALTER COLUMN "maintainerName" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "instance" ALTER COLUMN "maintainerEmail" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "instance" ALTER COLUMN "iconUrl" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "instance" ALTER COLUMN "faviconUrl" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "instance" ALTER COLUMN "themeColor" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "clip" ALTER COLUMN "description" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "note" ALTER COLUMN "channelId" DROP DEFAULT`),
+            queryRunner.query(`ALTER TABLE "abuse_user_report" ALTER COLUMN "comment" DROP DEFAULT`),
+
+            queryRunner.query(`CREATE INDEX "IDX_315c779174fe8247ab324f036e" ON "drive_file" ("isLink")`),
+            queryRunner.query(`CREATE INDEX "IDX_f22169eb10657bded6d875ac8f" ON "note" ("channelId")`),
+            queryRunner.query(`CREATE INDEX "IDX_a9021cc2e1feb5f72d3db6e9f5" ON "abuse_user_report" ("targetUserId")`),
+
+            queryRunner.query(`DELETE FROM "abuse_user_report" WHERE "targetUserId" NOT IN (SELECT "id" FROM "user")`).then(() => {
+                queryRunner.query(`ALTER TABLE "abuse_user_report" ADD CONSTRAINT "FK_a9021cc2e1feb5f72d3db6e9f5f" FOREIGN KEY ("targetUserId") REFERENCES "user"("id") ON DELETE CASCADE ON UPDATE NO ACTION`);
+            }),
+
+            queryRunner.query(`ALTER TABLE "poll" ADD CONSTRAINT "UQ_da851e06d0dfe2ef397d8b1bf1b" UNIQUE ("noteId")`),
+            queryRunner.query(`ALTER TABLE "user_keypair" ADD CONSTRAINT "UQ_f4853eb41ab722fe05f81cedeb6" UNIQUE ("userId")`),
+            queryRunner.query(`ALTER TABLE "user_profile" ADD CONSTRAINT "UQ_51cb79b5555effaf7d69ba1cff9" UNIQUE ("userId")`),
+            queryRunner.query(`ALTER TABLE "user_publickey" ADD CONSTRAINT "UQ_10c146e4b39b443ede016f6736d" UNIQUE ("userId")`),
+            queryRunner.query(`ALTER TABLE "promo_note" ADD CONSTRAINT "UQ_e263909ca4fe5d57f8d4230dd5c" UNIQUE ("noteId")`),
+
+            queryRunner.query(`ALTER TABLE "page" RENAME CONSTRAINT "FK_3126dd7c502c9e4d7597ef7ef10" TO "FK_a9ca79ad939bf06066b81c9d3aa"`),
+
+            queryRunner.query(`ALTER TYPE "public"."user_profile_mutingnotificationtypes_enum" ADD VALUE 'pollEnded' AFTER 'pollVote'`),
+        ]);
+    }
+
+    async down(queryRunner) {
+        await Promise.all([
+            // There is no ALTER TYPE REMOVE VALUE query, so the reverse operation is a bit more complex
+            queryRunner.query(`UPDATE "user_profile" SET "mutingNotificationTypes" = array_remove("mutingNotificationTypes", 'pollEnded')`)
+            .then(() =>
+                queryRunner.query(`CREATE TYPE "public"."user_profile_mutingnotificationtypes_enum_old" AS ENUM('follow', 'mention', 'reply', 'renote', 'quote', 'reaction', 'pollVote', 'receiveFollowRequest', 'followRequestAccepted', 'groupInvited', 'app')`)
+            ).then(() =>
+                queryRunner.query(`ALTER TABLE "user_profile" ALTER COLUMN "mutingNotificationTypes" DROP DEFAULT`)
+            ).then(() =>
+                queryRunner.query(`ALTER TABLE "user_profile" ALTER COLUMN "mutingNotificationTypes" TYPE "public"."user_profile_mutingnotificationtypes_enum_old"[] USING "mutingNotificationTypes"::"text"::"public"."user_profile_mutingnotificationtypes_enum_old"[]`)
+            ).then(() =>
+                queryRunner.query(`ALTER TABLE "user_profile" ALTER COLUMN "mutingNotificationTypes" SET DEFAULT '{}'`)
+            ).then(() =>
+                queryRunner.query(`DROP TYPE "public"."user_profile_mutingnotificationtypes_enum"`)
+            ).then(() =>
+                queryRunner.query(`ALTER TYPE "public"."user_profile_mutingnotificationtypes_enum_old" RENAME TO "user_profile_mutingnotificationtypes_enum"`)
+            ),
+
+            queryRunner.query(`ALTER TABLE "page" RENAME CONSTRAINT "FK_a9ca79ad939bf06066b81c9d3aa" TO "FK_3126dd7c502c9e4d7597ef7ef10"`),
+
+            queryRunner.query(`ALTER TABLE "promo_note" DROP CONSTRAINT "UQ_e263909ca4fe5d57f8d4230dd5c"`),
+            queryRunner.query(`ALTER TABLE "user_publickey" DROP CONSTRAINT "UQ_10c146e4b39b443ede016f6736d"`),
+            queryRunner.query(`ALTER TABLE "user_profile" DROP CONSTRAINT "UQ_51cb79b5555effaf7d69ba1cff9"`),
+            queryRunner.query(`ALTER TABLE "user_keypair" DROP CONSTRAINT "UQ_f4853eb41ab722fe05f81cedeb6"`),
+            queryRunner.query(`ALTER TABLE "poll" DROP CONSTRAINT "UQ_da851e06d0dfe2ef397d8b1bf1b"`),
+
+            queryRunner.query(`ALTER TABLE "abuse_user_report" ALTER COLUMN "comment" SET DEFAULT '{}'`),
+            queryRunner.query(`ALTER TABLE "abuse_user_report" DROP CONSTRAINT "FK_a9021cc2e1feb5f72d3db6e9f5f"`),
+
+            queryRunner.query(`DROP INDEX "public"."IDX_a9021cc2e1feb5f72d3db6e9f5"`),
+            queryRunner.query(`DROP INDEX "public"."IDX_f22169eb10657bded6d875ac8f"`),
+            queryRunner.query(`DROP INDEX "public"."IDX_315c779174fe8247ab324f036e"`),
+
+            /* DEFAULT's are not set again because if the column can be NULL, then DEFAULT NULL is not necessary.
+            see also https://github.com/typeorm/typeorm/issues/7579#issuecomment-835423615 */
+
+            queryRunner.query(`CREATE INDEX "IDX_note_on_channelId_and_id_desc" ON "note" ("id", "channelId") `),
+            queryRunner.query(`ALTER INDEX "public"."IDX_c8cc87bd0f2f4487d17c651fbf" RENAME TO "IDX_seoignmeoprigmkpodgrjmkpormg"`),
+        ]);
+    }
+}
diff --git a/packages/backend/src/models/entities/access-token.ts b/packages/backend/src/models/entities/access-token.ts
index 69cdc49ce..c6e2141a4 100644
--- a/packages/backend/src/models/entities/access-token.ts
+++ b/packages/backend/src/models/entities/access-token.ts
@@ -15,7 +15,6 @@ export class AccessToken {
 
 	@Column('timestamp with time zone', {
 		nullable: true,
-		default: null,
 	})
 	public lastUsedAt: Date | null;
 
@@ -29,7 +28,6 @@ export class AccessToken {
 	@Column('varchar', {
 		length: 128,
 		nullable: true,
-		default: null,
 	})
 	public session: string | null;
 
@@ -52,7 +50,6 @@ export class AccessToken {
 	@Column({
 		...id(),
 		nullable: true,
-		default: null,
 	})
 	public appId: App['id'] | null;
 
@@ -65,21 +62,18 @@ export class AccessToken {
 	@Column('varchar', {
 		length: 128,
 		nullable: true,
-		default: null,
 	})
 	public name: string | null;
 
 	@Column('varchar', {
 		length: 512,
 		nullable: true,
-		default: null,
 	})
 	public description: string | null;
 
 	@Column('varchar', {
 		length: 512,
 		nullable: true,
-		default: null,
 	})
 	public iconUrl: string | null;
 
diff --git a/packages/backend/src/models/entities/auth-session.ts b/packages/backend/src/models/entities/auth-session.ts
index b82585620..295d1b486 100644
--- a/packages/backend/src/models/entities/auth-session.ts
+++ b/packages/backend/src/models/entities/auth-session.ts
@@ -23,7 +23,7 @@ export class AuthSession {
 		...id(),
 		nullable: true,
 	})
-	public userId: User['id'];
+	public userId: User['id'] | null;
 
 	@ManyToOne(type => User, {
 		onDelete: 'CASCADE',
diff --git a/packages/backend/src/models/entities/clip.ts b/packages/backend/src/models/entities/clip.ts
index da6b3c7a7..1386684c3 100644
--- a/packages/backend/src/models/entities/clip.ts
+++ b/packages/backend/src/models/entities/clip.ts
@@ -37,7 +37,7 @@ export class Clip {
 	public isPublic: boolean;
 
 	@Column('varchar', {
-		length: 2048, nullable: true, default: null,
+		length: 2048, nullable: true,
 		comment: 'The description of the Clip.',
 	})
 	public description: string | null;
diff --git a/packages/backend/src/models/entities/drive-file.ts b/packages/backend/src/models/entities/drive-file.ts
index 3d375f0e3..a636d1d51 100644
--- a/packages/backend/src/models/entities/drive-file.ts
+++ b/packages/backend/src/models/entities/drive-file.ts
@@ -79,7 +79,6 @@ export class DriveFile {
 	})
 	public properties: { width?: number; height?: number; orientation?: number; avgColor?: string };
 
-	@Index()
 	@Column('boolean')
 	public storedInternal: boolean;
 
diff --git a/packages/backend/src/models/entities/emoji.ts b/packages/backend/src/models/entities/emoji.ts
index b72ca7233..7332dd185 100644
--- a/packages/backend/src/models/entities/emoji.ts
+++ b/packages/backend/src/models/entities/emoji.ts
@@ -36,6 +36,7 @@ export class Emoji {
 
 	@Column('varchar', {
 		length: 512,
+		default: '',
 	})
 	public publicUrl: string;
 
diff --git a/packages/backend/src/models/entities/instance.ts b/packages/backend/src/models/entities/instance.ts
index bb24d6b30..7ea923438 100644
--- a/packages/backend/src/models/entities/instance.ts
+++ b/packages/backend/src/models/entities/instance.ts
@@ -107,53 +107,53 @@ export class Instance {
 	public isSuspended: boolean;
 
 	@Column('varchar', {
-		length: 64, nullable: true, default: null,
+		length: 64, nullable: true,
 		comment: 'The software of the Instance.',
 	})
 	public softwareName: string | null;
 
 	@Column('varchar', {
-		length: 64, nullable: true, default: null,
+		length: 64, nullable: true,
 	})
 	public softwareVersion: string | null;
 
 	@Column('boolean', {
-		nullable: true, default: null,
+		nullable: true,
 	})
 	public openRegistrations: boolean | null;
 
 	@Column('varchar', {
-		length: 256, nullable: true, default: null,
+		length: 256, nullable: true,
 	})
 	public name: string | null;
 
 	@Column('varchar', {
-		length: 4096, nullable: true, default: null,
+		length: 4096, nullable: true,
 	})
 	public description: string | null;
 
 	@Column('varchar', {
-		length: 128, nullable: true, default: null,
+		length: 128, nullable: true,
 	})
 	public maintainerName: string | null;
 
 	@Column('varchar', {
-		length: 256, nullable: true, default: null,
+		length: 256, nullable: true,
 	})
 	public maintainerEmail: string | null;
 
 	@Column('varchar', {
-		length: 256, nullable: true, default: null,
+		length: 256, nullable: true,
 	})
 	public iconUrl: string | null;
 
 	@Column('varchar', {
-		length: 256, nullable: true, default: null,
+		length: 256, nullable: true,
 	})
 	public faviconUrl: string | null;
 
 	@Column('varchar', {
-		length: 64, nullable: true, default: null,
+		length: 64, nullable: true,
 	})
 	public themeColor: string | null;
 
diff --git a/packages/backend/src/models/entities/meta.ts b/packages/backend/src/models/entities/meta.ts
index 4d58b5f04..80b5228bc 100644
--- a/packages/backend/src/models/entities/meta.ts
+++ b/packages/backend/src/models/entities/meta.ts
@@ -78,7 +78,7 @@ export class Meta {
 	public blockedHosts: string[];
 
 	@Column('varchar', {
-		length: 512, array: true, default: '{"/featured", "/channels", "/explore", "/pages", "/about-misskey"}',
+		length: 512, array: true, default: '{/featured,/channels,/explore,/pages,/about-misskey}',
 	})
 	public pinnedPages: string[];
 
@@ -346,14 +346,12 @@ export class Meta {
 
 	@Column('varchar', {
 		length: 8192,
-		default: null,
 		nullable: true,
 	})
 	public defaultLightTheme: string | null;
 
 	@Column('varchar', {
 		length: 8192,
-		default: null,
 		nullable: true,
 	})
 	public defaultDarkTheme: string | null;
diff --git a/packages/backend/src/models/entities/muting.ts b/packages/backend/src/models/entities/muting.ts
index b3a7e7a67..8f9e69063 100644
--- a/packages/backend/src/models/entities/muting.ts
+++ b/packages/backend/src/models/entities/muting.ts
@@ -17,7 +17,6 @@ export class Muting {
 	@Index()
 	@Column('timestamp with time zone', {
 		nullable: true,
-		default: null,
 	})
 	public expiresAt: Date | null;
 
diff --git a/packages/backend/src/models/entities/note.ts b/packages/backend/src/models/entities/note.ts
index da49d53b6..0ffeb85f6 100644
--- a/packages/backend/src/models/entities/note.ts
+++ b/packages/backend/src/models/entities/note.ts
@@ -53,8 +53,8 @@ export class Note {
 	})
 	public threadId: string | null;
 
-	@Column('varchar', {
-		length: 8192, nullable: true,
+	@Column('text', {
+		nullable: true,
 	})
 	public text: string | null;
 
@@ -179,7 +179,7 @@ export class Note {
 	@Index()
 	@Column({
 		...id(),
-		nullable: true, default: null,
+		nullable: true,
 		comment: 'The ID of source channel.',
 	})
 	public channelId: Channel['id'] | null;
diff --git a/packages/backend/src/models/entities/user-profile.ts b/packages/backend/src/models/entities/user-profile.ts
index f95cb144c..1778742ea 100644
--- a/packages/backend/src/models/entities/user-profile.ts
+++ b/packages/backend/src/models/entities/user-profile.ts
@@ -192,6 +192,7 @@ export class UserProfile {
 
 	@Column('jsonb', {
 		default: [],
+		comment: 'List of instances muted by the user.',
 	})
 	public mutedInstances: string[];
 
diff --git a/packages/backend/src/models/entities/user.ts b/packages/backend/src/models/entities/user.ts
index 29d9a0c2c..df92fb825 100644
--- a/packages/backend/src/models/entities/user.ts
+++ b/packages/backend/src/models/entities/user.ts
@@ -207,7 +207,7 @@ export class User {
 
 	@Column('boolean', {
 		default: false,
-		comment: 'Whether to show users replying to other users in the timeline',
+		comment: 'Whether to show users replying to other users in the timeline.',
 	})
 	public showTimelineReplies: boolean;