Flowify editOnInput.js

Summary:
Involved fixing two sketchy null checks. Nothing huge.

NOTE: There's lots of non flow-strict code that makes checks on keys. Empty string is an invalid key. This is the behavior right now, so I left it unchanged.

I extracted it to another module because I'll be using it to check the existence of keys in other parts of the code too.

Reviewed By: kedromelon

Differential Revision: D16595680

fbshipit-source-id: 13a08e3b2477ba46ba2a2c66089afe47edccb20a

Author: mrkev

src/component/handlers/edit/editOnInput.js

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  * @emails oncall+draft_js
  */
 
@@ -18,6 +18,7 @@ const DraftOffsetKey = require('DraftOffsetKey');
 const EditorState = require('EditorState');
 const UserAgent = require('UserAgent');
 
+const {notEmptyKey} = require('draftKeyUtils');
 const findAncestorOffsetKey = require('findAncestorOffsetKey');
 const gkx = require('gkx');
 const keyCommandPlainBackspace = require('keyCommandPlainBackspace');
@@ -158,8 +159,8 @@ function editOnInput(editor: DraftEditor, e: SyntheticInputEvent<>): void {
   });
 
   const entityKey = block.getEntityAt(start);
-  const entity = entityKey && content.getEntity(entityKey);
-  const entityType = entity && entity.getMutability();
+  const entity = notEmptyKey(entityKey) ? content.getEntity(entityKey) : null;
+  const entityType = entity != null ? entity.getMutability() : null;
   const preserveEntity = entityType === 'MUTABLE';
 
   // Immutable or segmented entities cannot properly be handled by the

src/component/utils/draftKeyUtils.js

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * Provides utilities for handling draftjs keys.
+ *
+ * @emails oncall+draft_js
+ * @flow strict-local
+ * @format
+ */
+
+'use strict';
+
+function notEmptyKey(key: ?string): boolean %checks {
+  return key != null && key != '';
+}
+
+module.exports = {
+  notEmptyKey,
+};