extract method: annotate newly created method @Nullable when applicable (IDEA-76767)

java/java-tests/testData/refactoring/extractMethod/NullableCheckVoid_after.java

@@ -1,3 +1,5 @@
+import org.jetbrains.annotations.Nullable;
+
 class Test {
    void foo() {
        Object o = newMethod();
@@ -5,6 +7,7 @@ class Test {
       System.out.println(o);
    }
 
+    @Nullable
     private Object newMethod() {
         Object o = "";
         for (int i = 0; i < 5; i++) {