Add .toBeNullish matcher

src/core/matchers/toBeNullish.js

@@ -0,0 +1,21 @@
+getJasmineRequireObj().toBeNullish = function() {
+  /**
+   * {@link expect} the actual value to be `null` or `undefined`.
+   * @function
+   * @name matchers#toBeNullish
+   * @since 5.6.0
+   * @example
+   * expect(result).toBeNullish():
+   */
+  function toBeNullish() {
+    return {
+      compare: function(actual) {
+        return {
+          pass: null === actual || void 0 === actual
+        };
+      }
+    };
+  }
+
+  return toBeNullish;
+};