IDEA-209947 Explain possible NPE

GitOrigin-RevId: dab1e1bfa33e2cdc0f1ab833f943bd24d171b882

java/java-tests/testData/inspection/dataFlow/tracker/NotNullParameter.java

@@ -1,6 +1,6 @@
 /*
 Value is always false (null == s)
-  Parameter 's' is annotated as 'non-null' (@NotNull String s)
+  Parameter 's' is annotated as 'non-null' (@NotNull)
  */
 import org.jetbrains.annotations.NotNull;
 

java/java-tests/testData/inspection/dataFlow/tracker/NpeAnnotation.java

@@ -0,0 +1,16 @@
+/*
+May be null (s)
+  's' was assigned (loadString())
+    Method 'loadString' is annotated as 'nullable' (@Nullable)
+ */
+
+import org.jetbrains.annotations.Nullable;
+
+class Test {
+  void test() {
+    String s = loadString();
+    System.out.println(<selection>s</selection>.trim());
+  }
+  
+  native @Nullable String loadString(); 
+}

java/java-tests/testData/inspection/dataFlow/tracker/NpeSimple.java

@@ -0,0 +1,14 @@
+/*
+May be null (s)
+  An execution might exist where:
+    's' is known to be 'null' from line #9 (s == null)
+ */
+
+class Test {
+  void test(String s) {
+    if (s == null) {
+      System.out.println(s);
+    }
+    System.out.println(<selection>s</selection>.trim());
+  }
+}

java/java-tests/testData/inspection/dataFlow/tracker/NpeWithCast.java

@@ -0,0 +1,17 @@
+/*
+May be null (foo)
+  'foo' was assigned (getFoo())
+    Method 'getFoo' is annotated as 'nullable' (@Nullable)
+ */
+
+import org.jetbrains.annotations.Nullable;
+
+class Test {
+
+  void test(Object x) {
+    String foo = (String)getFoo();
+    System.out.println(<selection>foo</selection>.trim());
+  }
+
+  @Nullable native Object getFoo();
+}