fix: if surname or displayname are null, set to empty string for Koha

If the surname or displayname from Koha are null then we cannot insert
in to the aspen DB. We need to set these to empty strings in this case
so we can still create an aspen user. This is especially true for sso as
currently we cannot enrich koha users with IdP data as it uses screen
scraping.

Author: Jacobomara901

code/web/sys/Account/User.php

@@ -1115,6 +1115,12 @@ function insert($context = '') {
 		if ($this->firstname === null) {
 			$this->firstname = '';
 		}
+		if ($this->lastname === null) {
+			$this->lastname = '';
+		}
+		if ($this->displayName === null) {
+			$this->displayName = '';
+		}
 		if ($context == 'development') {
 			$this->source = 'development';
 			$this->homeLocationId = 0;