How to remove a Particular Field Value using Groovy In oracle Fusion

when the user create the return sales order the Order type from the original sales order is reflecting or defaulting into the return Sales order when they create it, Now I need to find a way to avoid this, like when they create the RMA the Order type Field should be blank or null.

How can we make a particular Field : ORDER TYPE, as a null or blank through Groovy Extension on SAVE or SUBMIT event?

If anyone knows Please answer