When will a court refuse to instruct on the defense of mistake of fact?

"In a criminal case, a trial court must instruct on the general principles of law relevant to the issues raised by the evidence." (People v. Earp (1999) 20 Cal.4th 826, 885.) "Included within this duty is the '. . . obligation to instruct on defenses, . . . and on the relationship of these defenses to the elements of the charged offense . . .' where '. . . it appears that the defendant is relying on such a defense, or if there is substantial evidence supportive of such a defense . . . .' " (People v. Stewart (1976) 16 Cal.3d 133, 140.) A trial court does not err in failing to instruct on a defense if there was no substantial

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evidence supporting it. (See People v. Tufunga (1999) 21 Cal.4th 935, 944.) We review de novo a trial court's decision to refuse to give an instruction. (People v. Waidla (2000) 22 Cal.4th 690, 733 [the decision to instruct is a "mixed question of law and fact that . . . is . . . predominantly legal" and "should be examined without deference"].)

The defense of mistake of fact requires that defendant had a mistaken belief "relate[d] to a set of circumstances which, if existent or true, would make the act charged an innocent act." (People v. Lawson (2013) 215 Cal.App.4th 108, 115.) "[I]f the mental state of the crime is a specific intent or knowledge, then the mistaken belief must only be actual." (Ibid.)