Moved NullAwayExample.java to libraries-3.

Updated the libraries-3 README

libraries-3/README.md

@@ -12,3 +12,4 @@ Remember, for advanced libraries like [Jackson](/jackson) and [JUnit](/testing-m
 - [Guide to the Cactoos Library](https://www.baeldung.com/java-cactoos)
 - [Parsing Command-Line Parameters with Airline](https://www.baeldung.com/java-airline)
 - [Introduction to cache2k](https://www.baeldung.com/java-cache2k)
+- [Using NullAway to Avoid NullPointerExceptions](https://www.baeldung.com/java-nullaway)

libraries-3/src/main/java/com/baeldung/nullaway/NullAwayExample.java

@@ -0,0 +1,24 @@
+package com.baeldung.nullaway;
+
+import com.baeldung.distinct.Person;
+
+public class NullAwayExample {
+
+    /*
+     * 1- NullAway will warn about yearsToRetirement method
+     * 2- Uncomment @Nullable in printAge and NullAway will warn about this method
+     * 3- Add a standard null check to be NullAway compliant
+     * 4- Build will be SUCCESS
+     */
+
+    static Integer getAge(/*@Nullable*/ Person person) {
+        return person.getAge();
+    }
+
+    Integer yearsToRetirement() {
+        Person p = null;
+        // ... p never gets set correctly...
+        return 65 - getAge(p);
+    }
+
+}