Fix MIDIMessageEvent.data incorrectly typed as nullable

tsc/internal/bundled/libs/lib.dom.d.ts

@@ -23616,7 +23616,7 @@ interface MIDIMessageEvent extends Event {
      *
      * [MDN Reference](https://developer.mozilla.org/docs/Web/API/MIDIMessageEvent/data)
      */
-    readonly data: Uint8Array<ArrayBuffer> | null;
+    readonly data: Uint8Array<ArrayBuffer>;
 }
 
 declare var MIDIMessageEvent: {

tsc/testdata/baselines/reference/compiler/midiMessageEventDataNotNullable.js

@@ -0,0 +1,17 @@
+//// [tests/cases/compiler/midiMessageEventDataNotNullable.ts] ////
+
+//// [midiMessageEventDataNotNullable.ts]
+declare const input: MIDIInput;
+
+input.onmidimessage = (event) => {
+    // `data` should not be nullable, so this should not error.
+    event.data[0];
+};
+
+
+//// [midiMessageEventDataNotNullable.js]
+"use strict";
+input.onmidimessage = (event) => {
+    // `data` should not be nullable, so this should not error.
+    event.data[0];
+};

tsc/testdata/baselines/reference/compiler/midiMessageEventDataNotNullable.symbols

@@ -0,0 +1,21 @@
+//// [tests/cases/compiler/midiMessageEventDataNotNullable.ts] ////
+
+=== midiMessageEventDataNotNullable.ts ===
+declare const input: MIDIInput;
+>input : Symbol(input, Decl(midiMessageEventDataNotNullable.ts, 0, 13))
+>MIDIInput : Symbol(MIDIInput, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
+
+input.onmidimessage = (event) => {
+>input.onmidimessage : Symbol(MIDIInput.onmidimessage, Decl(lib.dom.d.ts, --, --))
+>input : Symbol(input, Decl(midiMessageEventDataNotNullable.ts, 0, 13))
+>onmidimessage : Symbol(MIDIInput.onmidimessage, Decl(lib.dom.d.ts, --, --))
+>event : Symbol(event, Decl(midiMessageEventDataNotNullable.ts, 2, 23))
+
+    // `data` should not be nullable, so this should not error.
+    event.data[0];
+>event.data : Symbol(MIDIMessageEvent.data, Decl(lib.dom.d.ts, --, --))
+>event : Symbol(event, Decl(midiMessageEventDataNotNullable.ts, 2, 23))
+>data : Symbol(MIDIMessageEvent.data, Decl(lib.dom.d.ts, --, --))
+
+};
+

tsc/testdata/baselines/reference/compiler/midiMessageEventDataNotNullable.types

@@ -0,0 +1,24 @@
+//// [tests/cases/compiler/midiMessageEventDataNotNullable.ts] ////
+
+=== midiMessageEventDataNotNullable.ts ===
+declare const input: MIDIInput;
+>input : MIDIInput
+
+input.onmidimessage = (event) => {
+>input.onmidimessage = (event) => {    // `data` should not be nullable, so this should not error.    event.data[0];} : (this: MIDIInput, event: MIDIMessageEvent) => void
+>input.onmidimessage : ((this: MIDIInput, ev: MIDIMessageEvent) => any) | null
+>input : MIDIInput
+>onmidimessage : ((this: MIDIInput, ev: MIDIMessageEvent) => any) | null
+>(event) => {    // `data` should not be nullable, so this should not error.    event.data[0];} : (this: MIDIInput, event: MIDIMessageEvent) => void
+>event : MIDIMessageEvent
+
+    // `data` should not be nullable, so this should not error.
+    event.data[0];
+>event.data[0] : number
+>event.data : Uint8Array<ArrayBuffer>
+>event : MIDIMessageEvent
+>data : Uint8Array<ArrayBuffer>
+>0 : 0
+
+};
+

tsc/testdata/fixtures/lib/dom.generated.d.ts

@@ -23600,7 +23600,7 @@ interface MIDIMessageEvent extends Event {
      *
      * [MDN Reference](https://developer.mozilla.org/docs/Web/API/MIDIMessageEvent/data)
      */
-    readonly data: Uint8Array<ArrayBuffer> | null;
+    readonly data: Uint8Array<ArrayBuffer>;
 }
 
 declare var MIDIMessageEvent: {

tsc/testdata/tests/cases/compiler/midiMessageEventDataNotNullable.ts

@@ -0,0 +1,9 @@
+// @strict: true
+// @lib: dom,es2015
+
+declare const input: MIDIInput;
+
+input.onmidimessage = (event) => {
+    // `data` should not be nullable, so this should not error.
+    event.data[0];
+};