Handling NULL value in XML using getStringVal

Hi,
I have below query which works fine if column 'XML_COL' has values. This select statement fails if the value is NULL for

select xmltype(t.xml_col).extract('//fax/text()').getStringVal() from mytab t

How to handle rows with NULL values in the column 'XML_COL'.

Why not add ato your statement?

Unfortunately I need all the values as this SELECT is part of another SELECT

added the CASE statement in SELECT statemnet to first check if the value is NULL or NOT. This is working fine.
Thanks

select
CASE WHEN
t.xml_col IS NULL THEN NULL
ELSE
xmltype(t.xml_col).extract('//fax/text()').getStringVal()
END
from mytab t