docs: private static FunctionDescriptor findFunction(String functionName,
                                                     Type returnType,
                                                     Type[] parameterType) {
          m_logger.debug("Looking for UDF " + functionName);
          FunctionDescriptor fd = FunctionDescriptor.m_by_LC_name.get(functionName);
          if (fd == null) {
              m_logger.debug("    Not defined in by_LC_name.  Maybe it's saved.");
              fd = FunctionDescriptor.m_saved_functions.get(functionName);
          }
          if (fd != null && functionMatches(fd, returnType, parameterType) ) {
              m_logger.debug("    " + functionName + " is defined or saved.  id == " + fd.getId());
              return fd;
          }
          m_logger.debug("    " + functionName + " is not defined or saved.");
          return null;
      }