Closes google#18512

Fixing condition in vailidation.py.

Course3/Lab4/validations.py

@@ -5,7 +5,7 @@
 def validate_user(username, minlen):
     """Checks if the received username matches the required conditions."""
     if type(username) != str:
-        raise TypeError("username must be a string")
+        raise TypeError("username must be a string ")
     if minlen < 1:
         raise ValueError("minlen must be at least 1")