You could combine the EMPLOYEE and TITLE tables in the Data Source View with a Named Query and handle the null values there with something like

SELECT EMPLOYEE.emp_id,

ISNULL(EMPLOYEE.title_id,-1) AS title_id,

ISNULL(TITLE.title_name,'Unknown') AS title_name

FROM EMPLOYEE

LEFT OUTER JOIN

TITLE

ON EMPLOYEE.title_id = TITLE.title_id