I had also faced the same issue recently. As I'm working with PostgreSQL database while inserting the data from Excel (.xlsx) file.
The PostgreSQL does not support zero in characters or 0x00 (unlike Oracle). You have to replace such chars with space or anything else.
In order to do so, you have to implement an expression in tMap to handle such situations.
Use below expression:
row1.your_column_name.replace("\\x00", " ")
For reference, follow below link:
This work for me. Give it a try.