JS: Consider empty regexp to be obviously empty

Author: asgerf

javascript/ql/src/RegExp/RegExpAlwaysMatches.ql

@@ -54,6 +54,8 @@ predicate isUniversalRegExp(RegExpTerm term) {
     or
     child.(RegExpCharacterClass).isUniversalClass()
   )
+  or
+  term.(RegExpSequence).getNumChild() = 0
 }
 
 /**

javascript/ql/test/query-tests/RegExp/RegExpAlwaysMatches/tst.js

@@ -83,10 +83,10 @@ function nonWordBoundary(x) {
 }
 
 function emptyRegex(x) {
-  return new RegExp("").test(x); // NOT OK
+  return new RegExp("").test(x); // OK
 }
 
 function parserTest(x) {
   /(\w\s*:\s*[^:}]+|#){|@import[^\n]+(?:url|,)/.test(x); // OK
-  /^((?:a{0,2}|-)|\w\{\d,\d\})+X$/.text(x); // ok 
-}
+  /^((?:a{0,2}|-)|\w\{\d,\d\})+X$/.text(x); // ok
+}