Problem with regenerating empty param docstring

[dohsimpson]

First of all, thanks for this great project! I'm seeing undesired behaviors when trying to run pyment twice in a row with the following function:

def fun(a, b):
    pass

The first run generates the following code:

def fun(a, b):
    """
    
    :param a:
    :param b:
    
    """
    pass

Run it again on the same file gives:

def fun(a, b):
    """
    
    :param a: param b:
    :param b:
    
    """
    pass

Whereas I am expecting the second run to not modify anything. However, running it a third time would not generate a patch.

[dadadel]

Indeed this is a bug. I will address this. Thanks!

[dadadel]

This is a specific case of more general issue #95