code: @Nullable
    public static EUBLTRDocumentType getDocumentTypeOfImplementationClass (@Nullable final Class <?> aImplClass)
    {
      if (aImplClass == null)
        return null;
      return ArrayHelper.findFirst (EUBLTRDocumentType.values (),
                                    eDocType -> eDocType.getImplementationClass ().equals (aImplClass));
    }
docs: Get the UBLTR document type matching the passed implementation class.
  
  @param aImplClass
  The implementation class to use. May be <code>null</code>.
  @return <code>null</code> if the implementation class is <code>null</code>
  or if no UBLTR document type has the specified implementation
  class.