public static @Nullable String suggestPrefix(XmlFile file, @Nullable String namespace) {
    if (namespace == null) {
      return null;
    }
    for (XmlSchemaProvider provider : XmlSchemaProvider.getAvailableProviders(file)) {
      String prefix = provider.getDefaultPrefix(namespace, file);
      if (prefix != null) {
        return prefix;
      }
    }
    return null; 
  }
public static @Nullable String suggestPrefix(XmlFile file, @Nullable String namespace)