code: public MockVolume deleteVolume(final String volumeId) {
  
          if (volumeId != null && allMockVolumes.containsKey(volumeId)) {
              return  allMockVolumes.remove(volumeId);
          }
  
          return null;
      }
docs: Delete Mock Volume.
  
  @param volumeId
  volumeId to be deleted
  @return Mock volume.