Objects are not linked associatively. The data in the internal tables is. The only way to suppress null values document wide is to remove them in the script so there are no null values at all. That's not always possible since missing values are also treated as nulls. See this blog post: The Importance of Nothing
Thank you for your comment Gysbert,
you're totally right about, I did not express my self in a proper way.
Unfortunately I cannot apply your suggestion since my document serves to multiple purposes (removing combinations of data that lead to null value would restrict other analysis' scope)
Any other way to achieve the result?
As Gysbert said, the charts are only linked by the available data to each other, i.e. selections in one will be reflected in each other (assuming not using set analysis, alternate states etc.. just plain default mode).
If you suppress dimension values in a chart by making use conditions etc. you would need to apply a similar logic to the other charts if you expect to see the same dimension / field values only.
For a list box, you can use a field expression (select <expression> from the field drop down list), then use something like
=if( len(trim(ShippedDate)), Customer)
or what ever works for a calculated dimension to show the customers you want to show.