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

escapeRegExp.js

@@ -22,7 +22,7 @@ const reHasRegExpChar = RegExp(reRegExpChar.source)
 function escapeRegExp(string) {
   return (string && reHasRegExpChar.test(string))
     ? string.replace(reRegExpChar, '\\$&')
-    : string
+    : (string || '')
 }
 
 export default escapeRegExp