diff --git a/src/lib.rs b/src/lib.rs
index 2c5d630..43768bb 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -54,6 +54,7 @@
 //! * select
 //! * macro
 //! * env
+//! * NULL
 //!
 //! ### Primitive types
 //!
@@ -81,6 +82,12 @@
 //! "I'm a \"fine\" looking string"; // escaped quotes in a string.
 //! ```
 //!
+//! * A NULL is an empty type. It represents no value.
+//!
+//! ```ucg
+//! let empty = NULL;
+//! ```
+//!
 //! ### Complex types
 //!
 //! ucg has two complex data types, Lists and Tuples.