Persistent null accross one-to-many join

Hello community.
My problem is complex.

- My Table 1 is a fact table where actors appear many time. Sometime data is incomplete and I have some null instead of the actor CODE. I set up a replacement for null to "Undetermined" ( "(null)" are not aesthetic in th final reporting) in Power Query in this Table.

- My Table 2 is a dimension Table where I get the actor NAME with them code. So I create a one-to-many join between Table 1 and 2 to have the proper name in the final reporting.

My problem is I dont want to have (null) in my segments and visuals. When I use the CODE (from Table 1), (null) is replaced with"Undetermined" as intended. But after the join, when I decide to use the proper NAME (from Table 2), I didnt find a way to avoid the (null) label in visuals. 

Does someone know a solution ? 

Thank you for your reading,

LZ