How have the courts interpreted the doctrine of estoppel in this case?

[161 Cal.App.2d 438] The argued suggestion that any default on appellant's part stems from the respondent's misleading conduct is not persuasive. The principles of estoppel, appropriately applied to certain inequitable situations, may sometimes furnish a proper excuse for dilatory action and it is certainly true that a governmental body should not be permitted to lead another party into a trap and then benefit from its own misconduct. But the doctrine of estoppel is not an omnibus defense, nor is it one which will automatically afford relief where an unfortunate situation is but the result of a party's own dereliction. As set forth in 18 Cal.Jur.2d, pages 406-407, 'four things are essential to the application of the doctrine: (1) the party to be estopped must know the facts; (2) he must intend that his conduct shall be acted on or must so act that the party asserting the estoppel has a right to believe it is so intended; (3) the latter must be ignorant of the true facts; and (4) he must rely on the former's conduct to his injury.' To reiterate these well-established essential is to refute any claim of estoppel in this case. Certainly the appellant was never in ignorance of the true facts, nor are the other elements of the doctrine here established. Of importance is the pronouncement of the court in Pacheco v. Clark, 44 Cal.App.2d 147, 153, 112 P.2d 67, 70: 'The doctrine of estoppel where the state is involved should not be lightly invoked.'