docs: public static <OPERATOR extends Operator<?>> OPERATOR validateImplementation(OPERATOR operator) {
          for (TypeVariable<?> var : Validate.notNull(operator, "operator").getClass().getTypeParameters()) {
              if (Types.resolveAt(operator, var) == null) {
                  throw new OperatorDefinitionException(operator, "Could not resolve %s against operator %s",
                      TypeUtils.toLongString(var), operator);
              }
          }
          return operator;
      }