Add test for empty option on command

Fixes tj#727

test/test.command.action.emptyOption.js

@@ -0,0 +1,20 @@
+/**
+ * Module dependencies.
+ */
+
+var program = require('../')
+  , should = require('should');
+
+var val = "some cheese"
+program
+  .name('test')
+  .command('mycommand')
+  .option('-c, --cheese [type]', 'optionally specify the type of cheese')
+  .action(function(cmd) {
+    val = cmd.cheese;
+  });
+
+program.parse(['node', 'test', 'mycommand', '--cheese', '']);
+
+val.should.equal('');
+