Property expressions must not be blank

editor/js/ui/utils.js

@@ -284,6 +284,9 @@ RED.utils = (function() {
         // in red/runtime/util.js
 
         var length = str.length;
+        if (length === 0) {
+            return false;
+        }
         var start = 0;
         var inString = false;
         var inBox = false;

red/runtime/util.js

@@ -133,6 +133,9 @@ function normalisePropertyExpression(str) {
     // in editor/js/ui/utils.js
 
     var length = str.length;
+    if (length === 0) {
+        throw new Error("Invalid property expression: zero-length");
+    }
     var parts = [];
     var start = 0;
     var inString = false;

test/red/runtime/util_spec.js

@@ -361,6 +361,7 @@ describe("red/util", function() {
         it("fail a[0].[1]",function() { testInvalid("a[0].[1]"); })
         it("fail a['']",function() { testInvalid("a['']"); })
         it("fail 'a.b'c",function() { testInvalid("'a.b'c"); })
+        it("fail <blank>",function() { testInvalid("");})
 
     });
 });