I got the below error while editing an assignment's settings. The assignment previously had date restrictions ie cut off date etc, i went into the settings, unticked the three check boxes in that section and hit update.f

Debug info: Column 'alwaysshowdescription' cannot be null
UPDATE mdl_assign SET name = ?,timemodified = ?,course = ?,intro = ?,introformat = ?,alwaysshowdescription = ?,submissiondrafts = ?,requiresubmissionstatement = ?,sendnotifications = ?,sendlatenotifications = ?,duedate = ?,cutoffdate = ?,allowsubmissionsfromdate = ?,grade = ?,completionsubmit = ?,teamsubmission = ?,requireallteammemberssubmit = ?,teamsubmissiongroupingid = ?,blindmarking = ?,attemptreopenmethod = ?,maxattempts = ? WHERE id=?
[array (
0 => 'file upload assignment',
1 => 1367289740,
2 => '2',
3 => '<p>upload something</p>',
4 => '1',
5 => NULL,
6 => '0',
7 => '0',
8 => '1',
9 => '1',
10 => 0,
11 => 0,
12 => 0,
13 => '100',
14 => 0,
15 => '0',
16 => '0',
17 => '0',
18 => '0',
19 => 'none',
20 => '-1',
21 => '3',
)]
Error code: dmlwriteexception
Stack trace:

line 426 of /lib/dml/moodle_database.php: dml_write_exception thrown
line 1195 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
line 1227 of /lib/dml/mysqli_native_moodle_database.php: call to mysqli_native_moodle_database->update_record_raw()
line 862 of /mod/assign/locallib.php: call to mysqli_native_moodle_database->update_record()
line 142 of /mod/assign/lib.php: call to assign->update_instance()
line 473 of /course/modlib.php: call to assign_update_instance()
line 260 of /course/modedit.php: call to update_moduleinfo()

Output buffer: <br /> <font size='1'><table class='xdebug-error xe-notice' dir='ltr' border='1' cellspacing='0' cellpadding='1'> <tr><th align='left' bgcolor='#f57900' colspan="5"><span style='background-color: #cc0000; color: #fce94f; font-size: x-large;'>( ! )</span> Notice: Undefined property: stdClass::$alwaysshowdescription in /home/andrew/Desktop/code/moodle/int/master/mod/assign/locallib.php on line <i>840</i></th></tr> <tr><th align='left' bgcolor='#e9b96e' colspan='5'>Call Stack</th></tr> <tr><th align='center' bgcolor='#eeeeec'>#</th><th align='left' bgcolor='#eeeeec'>Time</th><th align='left' bgcolor='#eeeeec'>Memory</th><th align='left' bgcolor='#eeeeec'>Function</th><th align='left' bgcolor='#eeeeec'>Location</th></tr> <tr><td bgcolor='#eeeeec' align='center'>1</td><td bgcolor='#eeeeec' align='center'>0.0024</td><td bgcolor='#eeeeec' align='right'>343632</td><td bgcolor='#eeeeec'>

Unknown macro: {main}

( )</td><td title='/home/andrew/Desktop/code/moodle/int/master/course/modedit.php' bgcolor='#eeeeec'>../modedit.php<b>:</b>0</td></tr> <tr><td bgcolor='#eeeeec' align='center'>2</td><td bgcolor='#eeeeec' align='center'>0.8328</td><td bgcolor='#eeeeec' align='right'>35597328</td><td bgcolor='#eeeeec'>update_moduleinfo( )</td><td title='/home/andrew/Desktop/code/moodle/int/master/course/modedit.php' bgcolor='#eeeeec'>../modedit.php<b>:</b>260</td></tr> <tr><td bgcolor='#eeeeec' align='center'>3</td><td bgcolor='#eeeeec' align='center'>0.9160</td><td bgcolor='#eeeeec' align='right'>35688784</td><td bgcolor='#eeeeec'>assign_update_instance( )</td><td title='/home/andrew/Desktop/code/moodle/int/master/course/modlib.php' bgcolor='#eeeeec'>../modlib.php<b>:</b>473</td></tr> <tr><td bgcolor='#eeeeec' align='center'>4</td><td bgcolor='#eeeeec' align='center'>0.9179</td><td bgcolor='#eeeeec' align='right'>35691560</td><td bgcolor='#eeeeec'>assign->update_instance( )</td><td title='/home/andrew/Desktop/code/moodle/int/master/mod/assign/lib.php' bgcolor='#eeeeec'>../lib.php<b>:</b>142</td></tr> </table></font>