Language customisation plugin database error when loading english (en) language pack

When loading the english (en) language pack for customisation, the progress bar loaded, and instead of completing and showing me the editing screen, the process crashed at 92% with a database error.

The error message is as follows:

Error writing to database

More information about this error
Debug info: Column 'original' cannot be null
INSERT INTO mdl_tool_customlang (lang,componentid,stringid,original,master,timemodified,outdated,local,timecustomized) VALUES(?,?,?,?,?,?,?,?,?)
[array (
0 => 'en',
1 => '165',
2 => 'typea',
3 => NULL,
4 => NULL,
5 => 1335428219,
6 => 0,
7 => NULL,
8 => NULL,
)]
Stack trace:

line 397 of /lib/dml/moodle_database.php: dml_write_exception thrown
line 893 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
line 935 of /lib/dml/mysqli_native_moodle_database.php: call to mysqli_native_moodle_database->insert_record_raw()
line 190 of /admin/tool/customlang/locallib.php: call to mysqli_native_moodle_database->insert_record()
line 60 of /admin/tool/customlang/index.php: call to tool_customlang_utils::checkout()

To reproduce the bug:
1. Open "Language -> Language Customisation" in the Site Administration Block
2. Select English (en)
3. Click "Open Language Pack for Editing"