checking if a string is null

[EyeTalion]

d is declared as a string and I want to check and see if it's null. IsNull is giving me an error, is there a function in .NET to check if a string is null?

If UCase(objDR("JOB_REQD_OPT_SP")) = "Y" And (IsNull(d) Or Trim(d) = "") Then