user_float does not support 0 or 0.0

[amp-bjorn]

When typing in 0 to the user_float function, nothing is returned, and the user is prompted for information again.

[Jasper-Harvey0]

Ah yes, the old '0.0' is a falsy value.

>>> "I am True" if float(0.0) else "I am False"
'I am False'

Follow the function calls through the labyrinth and you see that we perform this exact check on a float:

Changing to ret_val is not None will fix this.