@echo should reply with help when it receives no arguments

plugins/Utilities.py

@@ -122,6 +122,8 @@ class Utilities(callbacks.Privmsg):
 
         Returns the arguments given it.
         """
+        if not args:
+            raise callbacks.ArgumentError
         irc.reply(msg, ' '.join(args), prefixName=False)
 
     def action(self, irc, msg, args):

test/test_Utilities.py

@@ -61,6 +61,7 @@ class UtilitiesTestCase(PluginTestCase, PluginDocumentation):
         self.assertResponse('strconcat foo bar baz', 'foobar baz')
 
     def testEcho(self):
+        self.assertHelp('echo')
         self.assertResponse('echo foo', 'foo')
         m = self.getMsg('cpustats')
         self.assertResponse('echo "%s"' % m.args[1], m.args[1])