Why is this expressing to null?

[Evan0211]

I can't seem to figure out why this is expressing to null (-) instead of 0:

=IF(LEN(TRIM(fieldname)) = 0, 0 , Len(fieldname))

[Evan0211]

This also expresses to (-) instead of string null.

=if(isnull(fieldname), 'null', fieldname)