In In re Peterson (1943) 56 Cal.App.2d 791 the appellate court was called upon to interpret the meaning of Section 721, which was the predecessor of Section 652 and provided that prior to filing a petition in the juvenile court 'the probation officer . . . shall make such investigation as he deems necessary . . . .' In holding that it was not mandatory under Section 721 for the probation officer to make an investigation . . . before filing a petition, the reviewing court stated as follows: 'He is required to make only "such investigation as he deems necessary," which vests a discretion in him to make or not to make an investigation in certain cases. If he failed to make an investigation in this case we must presume that he was exercising the discretion given him under the statute.'