[BUG] mutable object as default values

[VukW]

In some places we are using {} as default function param values. However this is error-prone as these default values are mutable and can be modified unexpectedly during the call:

In [1]: def fun(d={}):
   ...:     d['count'] = d.get('count', 0) + 1
   ...:     print(d)
   ...:

In [2]: fun()
{'count': 1}

In [3]: fun()
{'count': 2}  # default value was modified

Right now it doesn't break anything, but it's worth to fix these cases, not using mutable objects as default values