Don't add a default to dataset if it doesn't exist
Don't add a default to dataset if it doesn't exist

If we use ".value()" instead, an empty default will not be added.

This fixes a weird bug that was occurring, most likely because the json
values in the object were shifting around, where the name and the label
would be wrong.

Signed-off-by: Patrick Avery <743342299f279e7a8c3ff5eb40671fce3e95f13a@kitware.com>

OpenChemistry/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz