README.md in airborne-0.1.16 vs README.md in airborne-0.1.17

@@ -43,9 +43,10 @@
 * `:float`
 * `:bool` or `:boolean`
 * `:string`
 * `:date`
 * `:object`
+* `:null`
 * `:array`
 * `:array_of_integers` or `:array_of_ints`
 * `:array_of_floats`
 * `:array_of_strings`
 * `:array_of_booleans` or `:array_of_bools`