Feature/fix yaml document seperator null

[Moep90]

Fixes issue #843

Proposed Changes

• Introduced SafeDumper as proposed here
• https://pyyaml.docsforge.com/master/api/yaml/representer/

[ramaro]

Hey @Moep90 sorry for the delay.

I see the intention here, but I personally make use of null in YAML when setting values to None in Kadet and honestly think that's the correct, expected behavior.

However I understand why this could be useful, so maybe we can add this as a feature behind a flag?

[MatteoVoges]

Hey @ramaro,

I'm working on this feature for the last hours and it seems like there is a problem with the yaml-representer.
I introduced the feature as a flag but the representer is loaded before the program starts and the flags/ arguments are read just after that.

So replacing the none-type-representer at runtime won't work. I have thought of some constructor overloading for the PrettyDumper class, so that it can be instantiated with different parameters for different representers etc.

What do you suggest?

[Moep90]

fixed with #861