Check before modifying polygon coordinates

Author: hackermd

src/api.js

@@ -743,25 +743,27 @@ class VLWholeSlideMicroscopyImageViewer {
     });
 
     this[_drawingSource].on(VectorEventType.CHANGEFEATURE, (e) => {
-      const geometry = e.feature.getGeometry();
-      const type = geometry.getType();
-      // The first and last point of a polygon must be identical. The last point
-      // is an implmentation detail and is hidden from the user in the graphical
-      // interface. However, we must update the last point in case the first
-      // piont has been modified by the user.
-      if (type === 'Polygon') {
-        // NOTE: Polyon in GeoJSON format contains an array of geometries,
-        // where the first element represents the coordinates of the outer ring
-        // and the second element represents the coordinates of the inner ring
-        // (in our case the inner ring should not be present).
-        const layout = geometry.getLayout();
-        const coordinates = geometry.getCoordinates();
-        const firstPoint = coordinates[0][0];
-        const lastPoint = coordinates[0][coordinates[0].length-1];
-        if (firstPoint[0] !== lastPoint[0] || firstPoint[1] !== lastPoint[1]) {
+      if (e.feature !== undefined || e.feature !== null) {
+        const geometry = e.feature.getGeometry();
+        const type = geometry.getType();
+        // The first and last point of a polygon must be identical. The last point
+        // is an implmentation detail and is hidden from the user in the graphical
+        // interface. However, we must update the last point in case the first
+        // piont has been modified by the user.
+        if (type === 'Polygon') {
+          // NOTE: Polyon in GeoJSON format contains an array of geometries,
+          // where the first element represents the coordinates of the outer ring
+          // and the second element represents the coordinates of the inner ring
+          // (in our case the inner ring should not be present).
+          const layout = geometry.getLayout();
+          const coordinates = geometry.getCoordinates();
+          const firstPoint = coordinates[0][0];
+          const lastPoint = coordinates[0][coordinates[0].length-1];
+          if (firstPoint[0] !== lastPoint[0] || firstPoint[1] !== lastPoint[1]) {
             coordinates[0][coordinates[0].length-1] = firstPoint;
             geometry.setCoordinates(coordinates, layout);
             e.feature.setGeometry(geometry);
+          }
         }
       }
       publish(container, EVENT.ROI_MODIFIED, _getROIFromFeature(e.feature, this[_pyramidMetadata]));