copy resolve mut arg in funcs, methods

[ArtemIsmagilov]

this PR copy resolver problem #408

[ArtemIsmagilov]

I can, of course, strictly rewrite. At your discretion

if arg is None:
    arg = {}

[tobixen]

I think it's fine.

In most cases the dicts and lists passed as parameters are supposed to be read-only, then having {} or [] as default value isn't harmful. At the other hand, there is no way to enforce or even indicate that objects passed as parameters shouldn't be modified by a method. Passing None is definitively best practice, and the param or {}-style is compact and easily understandable.