code: static String buildPropertyKey(String propertyName, String[] prefixParts) {
          return buildPropertyKey(propertyName, Strings.UNDERSCORE, prefixParts);
      }
docs: Build the property key for the given name and prefix parts. The name is
  converted to CamelCase (underscore is used as a delimiter):
  
  <pre>
  MY_PROPERTY_NAME
  </pre>
  
  becomes
  
  <pre>
  myPropertyName
  </pre>
  
  @param propertyName
  @param prefixParts
  @return the key