How to create a PO with PAY ON CODE at PO headers as NULL using API?

Based on the below 2 doc.id's populated the PAY ON CODE column of the po header interface table with FND_API.G_MISS_CHAR [G_MISS_CHAR        CONSTANT    VARCHAR2(1) := chr(0)]

Customer APIs Issue: How to Null out an Existing Database Value Using an Update API? (Doc ID 287488.1)

How to Enter a Null Value (Clear a Value) For Any Column in Any BOM Interface Table? (Doc ID 264198.1)

l_PAY_ON_CODE := FND_API.G_MISS_CHAR

assigning the above value ensured value in application frontend to be shown as NULL (see snapshot)

But the length of the null value in column is 1 (probably bcos MISS CHAR is constant with varchar2(1) of length) but this assigning of MISS CHAR is not ensuring NULL in the column which is failing in the SQL where clause