M_INVALID_USERNAME to be consistent with the parameter name

synapse/api/errors.py

@@ -42,7 +42,7 @@ class Codes(object):
     EXCLUSIVE = "M_EXCLUSIVE"
     THREEPID_AUTH_FAILED = "M_THREEPID_AUTH_FAILED"
     THREEPID_IN_USE = "THREEPID_IN_USE"
-    INVALID_USER_NAME = "M_INVALID_USER_NAME"
+    INVALID_USERNAME = "M_INVALID_USERNAME"
 
 
 class CodeMessageException(RuntimeError):

synapse/handlers/register.py

@@ -54,7 +54,7 @@ class RegistrationHandler(BaseHandler):
                 400,
                 "User ID must only contain characters which do not"
                 " require URL encoding.",
-                Codes.INVALID_USER_NAME
+                Codes.INVALID_USERNAME
             )
 
         user = UserID(localpart, self.hs.hostname)