code: private Map<String, Map> volumes() {
      final ImmutableMap.Builder<String, Map> volumes = ImmutableMap.builder();
      for (final Map.Entry<String, String> entry : job.getVolumes().entrySet()) {
        final String path = entry.getKey();
        final String source = entry.getValue();
        if (Strings.isNullOrEmpty(source)) {
          volumes.put(path, new HashMap());
        }
      }
      return volumes.build();
    }
docs: Get container volumes.
  
  @return A set of container volumes.