storage: data.value column never contains NULL

neo/storage/database/mysqldb.py

@@ -197,7 +197,7 @@ class MySQLDatabaseManager(DatabaseManager):
                  id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
                  hash BINARY(20) NOT NULL,
                  compression TINYINT UNSIGNED NULL,
-                 value LONGBLOB NULL,
+                 value LONGBLOB NOT NULL,
                  UNIQUE (hash, compression)
              ) ENGINE=""" + engine)
 

neo/storage/database/sqlite.py

@@ -161,7 +161,7 @@ class SQLiteDatabaseManager(DatabaseManager):
                  id INTEGER PRIMARY KEY AUTOINCREMENT,
                  hash BLOB NOT NULL,
                  compression INTEGER NOT NULL,
-                 value BLOB NULL)
+                 value BLOB NOT NULL)
           """)
         q("""CREATE UNIQUE INDEX IF NOT EXISTS _data_i1 ON
                  data(hash, compression)