Store third-party annotations in a separate directory

third-party/annotations/javax/annotation/Nullable.java

@@ -0,0 +1,16 @@
+package javax.annotation;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+import javax.annotation.meta.TypeQualifierNickname;
+import javax.annotation.meta.When;
+
+@Documented
+@TypeQualifierNickname
+@Nonnull(when = When.UNKNOWN)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface Nullable {
+
+}