PickMapUpdOnlyIfNull property with Copy pickmap

Today I got to work up on a defect and as I was digging the root cause of the issue for the first time I came to know about this property :-)

Issue

A field exposed in parent applet on editing is not saving properly.The field had a static picklist. I was able to edit the record and I tried changing the value in the picklist but when I save the record the change is not reflected. I selected a new value but on saving the record it gets saved with the same old value

Rootcause

As usual I started with the checking whether the field is a joined field or not. Yeah the field was a joined field but luckily it was an implicit join. Then I moved to the pickmap section and in here everything was good. My field was EHP Med Business Type and the picklist field was value and that was expected. I proceeded to

the PickMapUpdOnlyIfNull property and this what I found there

I goggled to find out what it was and got my answer. This property makes a copy pick map to perform the copy operation only if the values of the fields specified in the pick map UpdOnlyIfNull are null in my case this property had the value EHP Med Business Type which means I could update EHP Med Business Type only when its null so when I tried to update it with another value the issue happened.

Inactivating this property fixed the issue :-)