Refactoring Method 56: replace exception with test (replace exception with test)

You throw an exception in the face of conditions that a caller can check in advance.Modify the caller so that the caller can check the caller before calling the function.

Motivation: the exception isProgramA major improvement in language. However, like many good things, exceptions will be abused and thus become no longer pleasant. "Exception" should only be used for abnormal and rare behaviors, that is, those that produce unexpected errors, rather than being a substitute for conditional checks. If you reasonably expect the caller to check a condition before calling the function, a test should be provided and the caller should use it.