Test if an array contains a specific number/string.

src/operators.js

@@ -5,7 +5,13 @@ var operators = {
     '<': (l, r) => l < r,
     '>=': (l, r) => l >= r,
     '<=': (l, r) => l <= r,
-    'contains': (l, r) => typeof l === 'string' ? l.indexOf(r) > -1 : false,
+	'contains': (l, r) => {
+        return typeof l !== 'undefined' 
+            ? typeof l.indexOf === 'function' 
+                ? l.indexOf(r) > -1 
+                : false 
+            : false;
+    },
     'and': (l, r) => l && r,
     'or': (l, r) => l || r
 };