fix: contains return false when left side equals null

src/operators.js

@@ -5,12 +5,10 @@ var operators = {
     '<': (l, r) => l < r,
     '>=': (l, r) => l >= r,
     '<=': (l, r) => l <= r,
-	'contains': (l, r) => {
-        return typeof l !== 'undefined' 
-            ? typeof l.indexOf === 'function' 
-                ? l.indexOf(r) > -1 
-                : false 
-            : false;
+    'contains': (l, r) => {
+        if (!l) return false;
+        if (typeof l.indexOf !== 'function') return false;
+        return l.indexOf(r) > -1;
     },
     'and': (l, r) => l && r,
     'or': (l, r) => l || r

test/syntax.js

@@ -14,7 +14,8 @@ describe('expression', function() {
             one: 1,
             two: 2,
             x: 'XXX',
-            y: undefined
+            y: undefined,
+            z: null
         });
     });
 
@@ -45,6 +46,7 @@ describe('expression', function() {
             expect(evalExp('x contains "X"', scope)).to.equal(true);
             expect(evalExp('1 contains "x"', scope)).to.equal(false);
             expect(evalExp('y contains "x"', scope)).to.equal(false);
+            expect(evalExp('z contains "x"', scope)).to.equal(false);
             expect(evalExp('(1..5) contains 3', scope)).to.equal(true);
             expect(evalExp('(1..5) contains 6', scope)).to.equal(false);
             expect(evalExp('"<=" == "<="', scope)).to.equal(true);