Ensure escapeRegExp returns an empty string when passing falsy values (#4432)

* Enable escapeRegExp tests

* Ensure escapeRegExp returns an empty string when passing falsy values

* Add parens around expression in escapeRegExp

test/escapeRegExp.test.js

@@ -0,0 +1,28 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { stubString } from './utils.js';
+import escapeRegExp from '../escapeRegExp.js';
+
+describe('escapeRegExp', function() {
+  var escaped = '\\^\\$\\.\\*\\+\\?\\(\\)\\[\\]\\{\\}\\|\\\\',
+      unescaped = '^$.*+?()[]{}|\\';
+
+  it('should escape values', function() {
+    assert.strictEqual(escapeRegExp(unescaped + unescaped), escaped + escaped);
+  });
+
+  it('should handle strings with nothing to escape', function() {
+    assert.strictEqual(escapeRegExp('abc'), 'abc');
+  });
+
+  it('should return an empty string for empty values', function() {
+    var values = [, null, undefined, ''],
+        expected = lodashStable.map(values, stubString);
+
+    var actual = lodashStable.map(values, function(value, index) {
+      return index ? escapeRegExp(value) : escapeRegExp();
+    });
+
+    assert.deepStrictEqual(actual, expected);
+  });
+});