fix(knex): remove sqlite error message

We don't want to show this error message as we know of this behaviour

See: https://knexjs.org/guide/query-builder.html#insert
Signed-off-by: Philip Molares <philip.molares@udo.edu>

backend/knexfile.ts

@@ -12,6 +12,7 @@ const config: { [key: string]: Knex.Config } = {
     connection: {
       filename: './hedgedoc.sqlite',
     },
+    useNullAsDefault: true,
     migrations: {
       directory: './src/database/migrations',
     },

backend/src/config/database.config.ts

@@ -84,6 +84,7 @@ export function getKnexConfig(databaseConfig: DatabaseConfig): Knex.Config {
         connection: {
           filename: databaseConfig.name,
         },
+        useNullAsDefault: true,
       };
     case DatabaseType.POSTGRES:
       return {