From f99ff7bc8226fed4ec66d91f30d80b2e7df31284 Mon Sep 17 00:00:00 2001
From: Michael Rauch <git.mra@miranet.ch>
Date: Thu, 27 May 2021 17:19:10 +0200
Subject: [PATCH] csvw: declaring null value on table level

---
 documentation/mapping-language.md | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/documentation/mapping-language.md b/documentation/mapping-language.md
index b9ad3cf..38b4083 100644
--- a/documentation/mapping-language.md
+++ b/documentation/mapping-language.md
@@ -84,7 +84,21 @@ When dealing with CSV files, sometimes a column that contains numbers will conta
 ```
 
 
+In order to apply a `null` value for all columns in a table, it can also be declared on the `logical-source` or `source-group` level:
 
+```
+logical-source airport {
+	type csv
+	source "airport"
+	null "X"
+
+	referenceables
+		id
+		stop
+		latitude
+		longitude
+}
+```
 
 
 ### source-group