Select records using crystal report with null condition

I was trying to filter the data in database with the following formula in my crystal report and one of the condition is to included the data even this, '{vw_CandidateProfile.Typ开发者_如何学编程e}' is null or empty string. But the formula below doesn't work. Any ideas?

{vw_CandidateProfile.Candidate_Code} = '881225095228' 
AND (
        {vw_CandidateProfile.Type} IN ['NGO','EDU','PRS','PPR','PPS','TTL','OTH'] 
        OR ISNULL({vw_CandidateProfile.Type})
    )

I have found the solution in which the IsNull() field has to comes before the field which is no IsNull().

{vw_CandidateProfile.Type} IN ['NGO','EDU','PRS','PPR','PPS','TTL','OTH'] 
    OR ISNULL({vw_CandidateProfile.Type})

becomes

ISNULL({vw_CandidateProfile.Type})
    OR {vw_CandidateProfile.Type} IN ['NGO','EDU','PRS','PPR','PPS','TTL','OTH'] 

Use formula: in Select Expert

ToText({vw_CandidateProfile.Type}) = ""