docs: protected <T extends Source>T getSourceImpl(
              Class<T> sourceClass) throws SQLException {
  
          if (JAXBSource.class.isAssignableFrom(sourceClass)) {
  
              // Must go first presently, since JAXBSource extends SAXSource
              // (purely as an implmentation detail) and it's not possible
              // to instantiate a valid JAXBSource with a Zero-Args
              // constructor(or any subclass thereof, due to the finality of
              // its private marshaller and context object attrbutes)
              // FALL THROUGH... will throw an exception
          } else if (StreamSource.class.isAssignableFrom(sourceClass)) {
              return createStreamSource(sourceClass);
          } else if ((sourceClass == null)
                     || DOMSource.class.isAssignableFrom(sourceClass)) {
              return createDOMSource(sourceClass);
          } else if (SAXSource.class.isAssignableFrom(sourceClass)) {
              return createSAXSource(sourceClass);
          } else if (StAXSource.class.isAssignableFrom(sourceClass)) {
              return createStAXSource(sourceClass);
          }
  
          throw Util.invalidArgument("sourceClass: " + sourceClass);
      }