code: private static List<String> getVariantKeys(String variantKeyPrefix, Collection<String> variants) {
  
  		List<String> variantKeys = new ArrayList<>();
  		for (String variant : variants) {
  			if (variant == null) {
  				variant = "";
  			}
  			if (variantKeyPrefix == null) {
  				variantKeys.add(variant);
  			} else {
  				variantKeys.add(variantKeyPrefix + variant);
  			}
  		}
  
  		return variantKeys;
  	}
docs: Returns the variant keys
  
  @param variantKeyPrefix
  the variant key prefix
  @param variants
  The variants