code: private Map<String, String> defaultMetadata() {
  
      final Builder<String, String> builder = ImmutableMap.builder();
  
      final Map<String, String> envVars = envVarSupplier.get();
  
      for (final Map.Entry<String, String> entry : DEFAULT_METADATA_ENVVARS.entrySet()) {
        final String envKey = entry.getKey();
        final String metadataKey = entry.getValue();
  
        final String envValue = envVars.get(envKey);
        if (envValue != null) {
          builder.put(metadataKey, envValue);
        }
      }
  
      return builder.build();
    }
docs: Metadata to associate with jobs by default. Currently sets some metadata based upon environment
  variables set when the CLI command is run.