New J2K: add some tests from obsolete issues

nj2k/testData/newJ2k/issues/kt-19340.java

@@ -0,0 +1,24 @@
+package test.nullabilityOnClassBoundaries;
+
+public class Item {
+    private String s1;
+    private String s2;
+
+    public void set(String s1, String s2) {
+        this.s1 = s1;
+        this.s2 = s2;
+    }
+}
+
+public class Reader {
+    public Item readItem(int n) {
+        Item item = new Item();
+        item.set(readString(n), null);
+        return item;
+    }
+
+    public String readString(int n) {
+        if (n <= 0) return null;
+        return Integer.toString(n);
+    }
+}