code: public void addExpectedSamples(Collection<String> sampleNames) {
          sampleNames.forEach(sample -> expectedSamplesPosition.putIfAbsent(sample, expectedSamplesPosition.size()));
      }
docs: Adds Sample names to the sample name set.
  Samples names are used to validate the completeness of a variant call.
  If a sample is not seen in the merged variant, the sample will be added as the registered default value.
  The default values are retrieved by {@link #getDefaultValue(String)} and set to {@link #DEFAULT_MISSING_GT} for GT_KEY.
  
  @param sampleNames Collection of sample names.