Panic when provided using struct object with null pointer field

[abdularis]

Error:
panic: reflect: call of reflect.Value.Interface on zero Value [recovered] panic: reflect: call of reflect.Value.Interface on zero Value

after quick reading, I think it has something to do with the usage of reflection, it does not check whether its valid reflect Value or not

[abdularis]

PR #59

[generikvault]

Hi,

thanks for the finding and solution.

the example in your pull request contains a typed nil value. This breaks the current check.

Typed nil can also occur for slices and maps.

Fixed it together with the same issue in the ? operator.

#60