diff --git a/docs/database_import/database_import.adoc b/docs/database_import/database_import.adoc
index 61644ec..640594d 100644
--- a/docs/database_import/database_import.adoc
+++ b/docs/database_import/database_import.adoc
@@ -16,6 +16,9 @@ The following tables can not be imported from a file and have to be manipulated
 * Experiment
 * Semester Experiment
 
+== Optional values
+If an attribute is optional/nullable and it has no value, then `NULL` (uppercase) has to be written.
+
 == How to understand this document
 === ID
 None of the mentioned ids in this document is meant as database id. The ids here only refer to the imported instances. The id in the database is assigned automatically.
diff --git a/docs/database_import/example_database_import.txt b/docs/database_import/example_database_import.txt
index 1d13a89..28d211f 100644
--- a/docs/database_import/example_database_import.txt
+++ b/docs/database_import/example_database_import.txt
@@ -11,10 +11,10 @@ id	number	program_label
 
 #Student
 student_number	first_name	last_name	uni_email	contact_email	bachelor_thesis	bachelor_thesis_work_group	note
-12233	Max	Mustermann	max@students.uni-mainz.de	maxi@protonmail.com			
-13344	Kevin	Bäcker	kevin@students.uni-mainz.de	kevi@protonmail.com			
-24455	Dora	Musterfrau	dora@students.uni-mainz.de		Acceleration on Mars	Physikum	Random note
-55122	Felix	Singer	fel@students.uni-mainz.de		Detector X	Physikum2	
+12233	Max	Mustermann	max@students.uni-mainz.de	maxi@protonmail.com	NULL	NULL	NULL
+13344	Kevin	Bäcker	kevin@students.uni-mainz.de	kevi@protonmail.com	NULL	NULL	NULL
+24455	Dora	Musterfrau	dora@students.uni-mainz.de	NULL	Acceleration on Mars	Physikum	Random note
+55122	Felix	Singer	fel@students.uni-mainz.de	NULL	Detector X	Physikum2	NULL
 
 #Group
 id	number	program_label