In Graves v. Roman (1952) 113 Cal.App.2d 584, plaintiff tried to "distinguish . . . 'trivial defect' authorities on the ground that they are all 'sidewalk' cases involving municipalities." (Id. at pp. 586-587.) The Graves court rejected that argument because "the authorities disclose that the underlying basis of the decisions is a practical recognition of the impossibility of maintaining heavily travelled surfaces in a perfect condition and that minor defects such as differences in elevation are bound to occur in spite of the exercise of reasonable care by the party having the duty of maintaining the area involved." (Ibid.)