don't show some java keywords in some java places, but show some keywords in some other places (e.g. IDEA-58589)

java/java-tests/testData/codeInsight/completion/keywords/NullInReturn-out.java

@@ -0,0 +1,8 @@
+
+public class Main {
+
+    public static Object main() {
+        return null<caret>
+
+    }
+}

java/java-tests/testData/codeInsight/completion/keywords/NullInReturn.java

@@ -0,0 +1,8 @@
+
+public class Main {
+
+    public static Object main() {
+        return nu<caret>
+
+    }
+}