diff --git a/etiquette/objects.py b/etiquette/objects.py
index 1caf1ff..8237acd 100644
--- a/etiquette/objects.py
+++ b/etiquette/objects.py
@@ -22,9 +22,13 @@ from . import helpers
 BAIL = sentinel.Sentinel('BAIL')
 
 def normalize_db_row(db_row, table):
+    if isinstance(db_row, dict):
+        return db_row
+
     if isinstance(db_row, (list, tuple)):
-        db_row = dict(zip(constants.SQL_COLUMNS[table], db_row))
-    return db_row
+        return dict(zip(constants.SQL_COLUMNS[table], db_row))
+
+    raise TypeError(f'db_row should be {dict}, {list}, or {tuple}, not {type(db_row)}.')
 
 class ObjectBase:
     def __init__(self, photodb):
@@ -581,7 +585,7 @@ class Bookmark(ObjectBase):
         url = url.strip()
 
         if not url:
-            raise ValueError(f'Invalid URL "{url}".')
+            raise ValueError(f'URL can not be blank.')
 
         return url
 
diff --git a/etiquette/photodb.py b/etiquette/photodb.py
index 1fbca5d..4ef1a73 100644
--- a/etiquette/photodb.py
+++ b/etiquette/photodb.py
@@ -1210,10 +1210,16 @@ class PDBUserMixin:
             raise exceptions.UserExists(existing_user)
 
     def assert_valid_password(self, password):
+        if not isinstance(password, bytes):
+            raise TypeError(f'Password must be {bytes}, not {type(password)}.')
+
         if len(password) < self.config['user']['min_password_length']:
             raise exceptions.PasswordTooShort(min_length=self.config['user']['min_password_length'])
 
     def assert_valid_username(self, username):
+        if not isinstance(username, str):
+            raise TypeError(f'Username must be {str}, not {type(username)}.')
+
         if len(username) < self.config['user']['min_username_length']:
             raise exceptions.UsernameTooShort(
                 username=username,
@@ -1287,7 +1293,7 @@ class PDBUserMixin:
         be workable but fails.
         '''
         if user_obj_or_id is None:
-            author_id = None
+            return None
 
         elif isinstance(user_obj_or_id, objects.User):
             if user_obj_or_id.photodb != self: