h3. Description
deleting mask modifiers (with shortcut) doesn't update the selected item correctly, when deleting the last item of the list view, the selection is out of bounds and trying to copy will result in a null ref exception.

h3. Repro Steps
Open WorldWorkspace/EnvTestProject
Open GettingStarted scene
select WorldAsset game object
double click on the object picker in the inspector to open the WorldAssetEditor window
select MaterialAssetLayer
in the inspector, click on the Mask tab
add a mask modifier by clicking on the + button (any type of modifier works)
select the modifier (click on it)
delete it (delete key or Ctrl+x)
copy (Ctrl+c)

h3. Actual Results
exception

h3. Expected Results
no exception

h3. Versions
h4. Editor Version
7000.0..0a10

h4. Git Repo Commit or Package Version