Wider usage of support function is_empty_string

[iosonopersia]

A wider usage of the function is_empty_string from support.py could be made across the entire project.

This function replaces this very common pattern when dealing with strings:

# The old:
if string is None or string == '':
    pass

# becomes:
if is_empty_string(string):
    pass

This makes much clearer the semantics of that conditional statement: the intention of the developer is easily and quickly understandable.