Hi,
I am trying to create a script to renumber parking spaces, I’m mid way though and I’m stuck trying to get the >= and > functions to work, both give me a Null. The == function gives a boolean result so not sure where I’m going wrong.
Many thanks in advance,
Luke
Hard to say without a screenshot… but i guess you have strings and not numbers, thus being able to compare directly but not higher/lower… Try using the Object.type node to see what type of objects your lists contain! 
‘‘Object.Type’’
Make sure you are comparing similar items. Do object.type on the flatten and see what you are working with may need to convert to number.
Mark is a string value (17a is an acceptable value). String.ToNumber should resolve the issue as others have noted.
There were some null values as the mark parameter had not been added to some of the families. Got there in the end, this allows me to renumber all my parking spaces in order when the layout changes and I need to add or remove a space!
Thanks for your help
