[REQ] [Go] Export Util isNil function

Created by: gcatanese

Is your feature request related to a problem? Please describe.

The function isNil generated in utils.go is not exported outside the package (unlike all other functions in the same file). This is a problem if you want to generate the model in a sub-directory: the generated models do not have access to the function.

Describe the solution you'd like

Export the function by renaming it to IsNil

Describe alternatives you've considered

At the moment you need to customise the template or the generated code locally.