ComposeConfig::config() null return not handled in InformationSchemaExtension (crash in Drush/CLI context)

Problem/Motivation

ComposeConfig::config() declares a nullable return type (?ImmutableConfig). It returns null when ComposeContext::getServerId() cannot resolve the server —
which happens in any CLI/Drush context because there is no active HTTP route to extract the graphql_server parameter from.

Steps to reproduce

1. Have graphql_compose with graphql_export enabled
2. Run drush graphql-export:schema or drush config:export
3. Observe the fatal error

Proposed resolution

Add a guard clause at the top of registerResolvers():

  $settings = ComposeConfig::config();
  if (!$settings) {
    return;
  }