Fixing reported issue jsonata-js#547. Added unit test coverage.

Author: kexuibm

src/jsonata.js

@@ -931,24 +931,26 @@ var jsonata = (function() {
                     };
                 }
 
-                var entry = {data: item, exprIndex: pairIndex};
-                if (groups.hasOwnProperty(key)) {
-                    // a value already exists in this slot
-                    if(groups[key].exprIndex !== pairIndex) {
-                        // this key has been generated by another expression in this group
-                        // when multiple key expressions evaluate to the same key, then error D1009 must be thrown
-                        throw {
-                            code: "D1009",
-                            stack: (new Error()).stack,
-                            position: expr.position,
-                            value: key
-                        };
-                    }
+                if (key !== undefined) {
+                    var entry = {data: item, exprIndex: pairIndex};
+                    if (groups.hasOwnProperty(key)) {
+                        // a value already exists in this slot
+                        if(groups[key].exprIndex !== pairIndex) {
+                            // this key has been generated by another expression in this group
+                            // when multiple key expressions evaluate to the same key, then error D1009 must be thrown
+                            throw {
+                                code: "D1009",
+                                stack: (new Error()).stack,
+                                position: expr.position,
+                                value: key
+                            };
+                        }
 
-                    // append it as an array
-                    groups[key].data = fn.append(groups[key].data, item);
-                } else {
-                    groups[key] = entry;
+                        // append it as an array
+                        groups[key].data = fn.append(groups[key].data, item);
+                    } else {
+                        groups[key] = entry;
+                    }
                 }
             }
         }
@@ -965,7 +967,7 @@ var jsonata = (function() {
                 env = createFrameFromTuple(environment, tuple);
             }
             var value = yield * evaluate(expr.lhs[entry.exprIndex][1], context, env);
-            if(typeof value !== 'undefined' && key !== 'undefined') {
+            if(typeof value !== 'undefined') {
                 result[key] = value;
             }
         }