diff --git a/src/main/java/com/github/creme332/model/ShapeManager.java b/src/main/java/com/github/creme332/model/ShapeManager.java
index bb52cf7..0d6499d 100644
--- a/src/main/java/com/github/creme332/model/ShapeManager.java
+++ b/src/main/java/com/github/creme332/model/ShapeManager.java
@@ -167,6 +167,10 @@ public void deleteShape(final int shapeIndex) {
     }
 
     public void editShape(final int oldShapeIndex, final ShapeWrapper newShape) {
+        if (newShape == null) {
+            throw new NullPointerException("Edit shape failed: Cannot replace a shape with null.");
+        }
+        
         final ShapeWrapper oldShape = shapes.get(oldShapeIndex);
         if (oldShapeIndex != -1) {
             shapes.set(oldShapeIndex, newShape);