Contributions - Create/Update Forces Non-required Amount Fields to Zero (should be NULL)

civicrm_contribution.fee_amount and net_amount fields have NULL default value in DB (this is correct). However, if you create or update a Contribution and leave these fields empty, the post_process function sets their value to 0.00. This is a bug - these fields should be left NULL is user doesn't enter a value. (If user enters 0, then saving as 0 is correct).

You can recreate this by editing any of the sample contribution records and clearing out the fee and net amount fields.