code: public static String getProjectId(Configuration conf) throws IOException {
      // Reference the default project ID as a backup.
      String projectId = conf.get(BigQueryConfiguration.OUTPUT_PROJECT_ID_KEY);
      if (Strings.isNullOrEmpty(projectId)) {
        projectId = conf.get(BigQueryConfiguration.PROJECT_ID_KEY);
      }
      if (Strings.isNullOrEmpty(projectId)) {
        throw new IOException(
            "Must supply a value for configuration setting: "
                + BigQueryConfiguration.OUTPUT_PROJECT_ID_KEY);
      }
      return projectId;
    }
docs: Gets the project id based on the given configuration. If the {@link
  BigQueryConfiguration#OUTPUT_PROJECT_ID_KEY} is missing, this resolves to referencing the
  {@link BigQueryConfiguration#PROJECT_ID_KEY} key.
  
  @param conf the configuration to reference the keys from.
  @return the project id based on the given configuration.
  @throws IOException if a required key is missing.