MDX - Filter on NULL Dimension Date and upToDate

Hi all , DimProject with the Project Name, Project Activation Date attribute Hierarchy. measures.production fact For some of the projects i have NULL activation date. and other's projects i have '2011-01-01 00:00.000' '2011-01-01 00:00.000' '2012-01-01 00:00.000' '2013-01-01 00:00.000' '2014-01-01 00:00.000' NULLNULLHow can i apply below filter 1) exclude the NULL or empty cells2) where project activation date <= '2013-01-01 00:00.000' should filter the rows give me '2011-01-01 00:00.000' '2012-01-01 00:00.000' '2013-01-01 00:00.000' how can i achieve this ..in MDXvineet