Avoid setting undefined options

Gruntfile.js

@@ -10,6 +10,10 @@ module.exports = function(grunt) {
         globalOption: 'foo'
       },
       testData: {
+        UNDEFINED_OPTION: function() {
+          // logic here might return undefined or not, but for testing we do
+          return undefined;
+        },
         TEST: 'test',
         data: 'bar'
       },
@@ -97,6 +101,12 @@ module.exports = function(grunt) {
     assert.equal(process.env.data, 'bar', 'data should be set');
     delete process.env.globalOption;
     delete process.env.data;
+
+    assert.equal(
+      process.env.hasOwnProperty('UNDEFINED_OPTION'),
+      false,
+      'UNDEFINED_OPTION should not be set on process.env'
+    );
   });
 
   grunt.registerTask('testOptions', function() {

package.json

@@ -29,6 +29,7 @@
   },
   "devDependencies": {
     "grunt": "~0.4.5",
+    "grunt-cli": "~1.2.0",
     "grunt-contrib-clean": "~0.6.0",
     "grunt-contrib-jshint": "~0.11.0",
     "grunt-jscs": "^1.5.0"
@@ -42,4 +43,4 @@
     "ini": "~1.3.0",
     "lodash": "~2.4.1"
   }
-}
+}

tasks/env.js

@@ -65,7 +65,10 @@ module.exports = function(grunt) {
       } else {
         var data = {};
         data[option] = typeof optionData === 'function' ? optionData() : optionData;
-        _.extend(process.env, data);
+
+        if (data[option] !== undefined) {
+          _.extend(process.env, data);
+        }
       }
     });
   }