Fixed NPE when showing tree cell popup and no cell is targeted. Fixes #194

core/src/main/java/com/github/weisj/darklaf/ui/cell/hint/CellHintPopupListener.java

@@ -90,6 +90,7 @@ public class CellHintPopupListener<T extends JComponent, I> extends MouseInputAd
         final boolean isEditing = cellContainer.isEditingCell(index);
         final Rectangle allocation = cellContainer.getAllocation();
         final Rectangle cellBounds = cellContainer.getCellBoundsAt(index, isEditing);
+        if (cellBounds != null && allocation != null) {
             final Rectangle visibleBounds = allocation.intersection(cellBounds);
             if (visibleBounds.contains(p)) {
                 final Component comp = cellContainer.getEffectiveCellRendererComponent(index, isEditing);
@@ -110,9 +111,10 @@ public class CellHintPopupListener<T extends JComponent, I> extends MouseInputAd
                         lastIndex = index;
                     }
                 }
-        } else {
-            lastIndex = null;
+                return;
             }
+        }
+        lastIndex = null;
         leave();
     }