public UnboundMethod build() {
      if (method != null) {
        return method;
      } else {
        throw new RuntimeException("Cannot find method: " + name);
      }
    }
Returns the first valid implementation as a UnboundMethod or throws a RuntimeError if there
is none.

@return a {@link UnboundMethod} with a valid implementation
@throws RuntimeException if no implementation was found
amoro-common/src/main/java/org/apache/amoro/utils/DynMethods.java