No warning or error log message when passing "None" to an input port

[sebastian-brunner]

If None is passed to an input port, which has a specific type (e.g. int), RAFCON won't print an error or warning message.

RAFCON does handle it correctly though: it replaces the invalid input port value by the default value of the input port.

This error especially emerges when using the core API. When using the GUI an error will be printed by the outcome port that creates a output value that does not match the output port type.

Credits: @stefanbuettner