If evidence is objected to at the trial on the ground that it is not within the issues made by the pleading, or if during the trial any defect, fault or omission in a pleading, either of form or substance, is called to the attention of the court, the court may allow the pleadings to be amended and shall do so freely when the presentation of the merits of the action will be subserved thereby and the objecting party fails to satisfy the court that the allowance of such amendment would prejudice him in maintaining his action or defense upon the merits. The court may grant a postponement to enable the objecting party to meet such evidence.