Move variable length field to fixed length

All,
I have a variable length field that I am moving to a fixed length field.
The fields are defined as:
D FldA S 128A Varying
D FldB S 30A

FldA = AB1234

My code is:
/Free
FldB = FldA;
After the move, FldB has a trailing NULL character.
When I look at it in DEBUG, I see 'C1C2F1F2F3F40040404040.....' for FldB.
FldA = 'C1C2F1F2F3F400000000..........................'

Release 7.1
Why am I getting the trailing NULL and how can I prevent it.

Thanks,