While reading EBCDIC file with Cobrix Library , noticed that it converts incorrectly as numbers for few Hexa value instead of null.

CopyBook:
RecordIdentifier PIC 9(1)
RecordName PIC x(10)

Sample Data:
Hex Value Cobrix Output Expected Output
f9 9 9
c4 4 null ( equivalent data -> D since it is number in copybook so it should null )
c5 5 null ( equivalent data -> E since it is number in copybook so it should null )
d6 null null

Could you please clarify why it is happening like this ?