Fix potential NPE issue

Signed-off-by: Taylor Smock <taylor.smock@kaart.com>

src/main/java/org/openstreetmap/josm/plugins/mapwithai/commands/MapWithAIAddCommand.java

@@ -163,8 +163,9 @@ public class MapWithAIAddCommand extends Command implements Runnable {
 
     public Collection<String> getSourceTags() {
         return sources.entrySet().parallelStream()
-                .filter(entry -> !editable.getPrimitiveById(entry.getKey()).isDeleted()).map(Entry::getValue)
-                .filter(Objects::nonNull).distinct().sorted().collect(Collectors.toList());
+                .filter(entry -> editable.getPrimitiveById(entry.getKey()) != null
+                        && !editable.getPrimitiveById(entry.getKey()).isDeleted())
+                .map(Entry::getValue).filter(Objects::nonNull).distinct().sorted().collect(Collectors.toList());
     }
 
     @Override