You could try:
zn([your data]) and plot this instead.
zn makes any nulls zero instead.
Missing domain members can be frustrating.
One option is to use custom SQL or a database view with the SQL UNION ALL command to add data rows with null measure values for all or missing dimensions. Null measure values will be ignored in most calculations but will fill out the domain of your dimensions. (The ALL keyword is important for better performance).
For some data types, such as dates and histogram bins, Tableau can pad the domain if you tell it, i.e. to show missing members of a dimension even if they have no data values. You can use aliases to give meaningful labels to histogram bins. Use the "show all values" menu option and/or the Analysis->Table Layout->Show All Rows (or Columns) menu item.
Sure would love to hear of other alternatives, because these two approaches don't fit every case.