IDEA-129331 False positive for possible NPE

java/java-tests/testData/inspection/dataFlow/fixture/RootThrowableCause.java

@@ -1,3 +1,6 @@
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.Nullable;
+
 class Doo {
 
   void foo(Throwable e) {
@@ -9,4 +12,18 @@ class Doo {
     }
   }
 
+}
+
+abstract class Test04 {
+  @Nullable
+  @Contract(pure = true)
+  abstract Test04 getParent();
+
+  Test04 getTopParent() {
+    Test04 top = this;
+    while (top.getParent() != null) {
+      top = top.getParent();
+    }
+    return top;
+  }
 }