fix($parser): string concatination with undefined model

Closes #988

1 files changed, 9 insertions, 1 deletions

diff --git a/src/ng/parse.js b/src/ng/parse.js
index be17e6ca..97aba113 100644
--- a/src/ng/parse.js
+++ b/src/ng/parse.js
@@ -5,7 +5,15 @@ var OPERATORS = {
     'true':function(){return true;},
     'false':function(){return false;},
     undefined:noop,
-    '+':function(self, locals, a,b){a=a(self, locals); b=b(self, locals); return (isDefined(a)?a:0)+(isDefined(b)?b:0);},
+    '+':function(self, locals, a,b){
+      a=a(self, locals); b=b(self, locals);
+      if (isDefined(a)) {
+        if (isDefined(b)) {
+          return a + b;
+        }
+        return a;
+      }
+      return isDefined(b)?b:undefined;},
     '-':function(self, locals, a,b){a=a(self, locals); b=b(self, locals); return (isDefined(a)?a:0)-(isDefined(b)?b:0);},
     '*':function(self, locals, a,b){return a(self, locals)*b(self, locals);},
     '/':function(self, locals, a,b){return a(self, locals)/b(self, locals);},