static @Nullable String fetchSchemaId(@NotNull PsiFile psiFile) {
    if (!(psiFile instanceof JsonFile)) return null;
    final Map<String, String> props = JsonSchemaFileValuesIndex.readTopLevelProps(psiFile.getFileType(), psiFile.getText());
    final String id = props.get(ID_CACHE_KEY);
    if (id != null && !JsonSchemaFileValuesIndex.NULL.equals(id)) return id;
    final String obsoleteId = props.get(OBSOLETE_ID_CACHE_KEY);
    return obsoleteId == null || JsonSchemaFileValuesIndex.NULL.equals(obsoleteId) ? null : obsoleteId;
  }
static @Nullable String fetchSchemaId(@NotNull PsiFile psiFile)