Migrate jest-get-type to TypeScript

[SimenB]

Summary

Build diff:

diff --git c/packages/jest-get-type/build/index.js w/packages/jest-get-type/build/index.js
index e3a0a41f1..15c318ee8 100644
--- c/packages/jest-get-type/build/index.js
+++ w/packages/jest-get-type/build/index.js
@@ -1,13 +1,11 @@
+'use strict';
+
 /**
  * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
- *
- *
  */
-'use strict';
-
 // get the type of a value with handling the edge cases like `typeof []`
 // and `typeof null`
 const getType = value => {
@@ -26,17 +24,19 @@ const getType = value => {
   } else if (typeof value === 'string') {
     return 'string';
   } else if (typeof value === 'object') {
-    if (value.constructor === RegExp) {
-      return 'regexp';
-    } else if (value.constructor === Map) {
-      return 'map';
-    } else if (value.constructor === Set) {
-      return 'set';
-    } else if (value.constructor === Date) {
-      return 'date';
+    if (value != null) {
+      if (value.constructor === RegExp) {
+        return 'regexp';
+      } else if (value.constructor === Map) {
+        return 'map';
+      } else if (value.constructor === Set) {
+        return 'set';
+      } else if (value.constructor === Date) {
+        return 'date';
+      }
     }
 
-    return 'object'; // $FlowFixMe https://github.com/facebook/flow/issues/1015
+    return 'object';
   } else if (typeof value === 'symbol') {
     return 'symbol';
   }

Test plan

Green CI

[github-actions]

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