THRIFT-4614: Generate missing @Nullable annotation (#1577)

Client: Java
diff --git a/compiler/cpp/src/thrift/generate/t_java_generator.cc b/compiler/cpp/src/thrift/generate/t_java_generator.cc
index 2db3c3f..67b4177 100644
--- a/compiler/cpp/src/thrift/generate/t_java_generator.cc
+++ b/compiler/cpp/src/thrift/generate/t_java_generator.cc
@@ -2359,6 +2359,7 @@
         if (is_deprecated) {
           indent(out) << "@Deprecated" << endl;
         }
+        indent(out) << java_nullable_annotation() << endl;
         indent(out) << "public java.util.Iterator<" << type_name(element_type, true, false)
                     << "> get" << cap_name;
         out << get_cap_name("iterator() {") << endl;