Added null check to find() call to prevent NullPointerException when running tests.

src/tests/gitlab/ckpt2/AVLTreeTests.java

@@ -139,6 +139,7 @@ public class AVLTreeTests extends TestsUtility {
 		// Check for accuracy
 		passed &= totalCount == (n * (n + 1)) / 2 * 5;
 		passed &= tree.size() == n;
+		passed &= tree.find("00851") != null;
 		passed &= tree.find("00851") == 4260;
 		
 		return passed ? 1 : 0;