Checking before trying to array merge.
$eventsManagementSettings = $wpdb->get_row( "SELECT * FROM ".GLM_MEMBERS_EVENTS_PLUGIN_DB_PREFIX."management WHERE id = 1", ARRAY_A );
// Grab the new email_notification to_email and from_email to add to these (override)
$emailNotifications = $wpdb->get_row( "SELECT * FROM ".GLM_MEMBERS_EVENTS_PLUGIN_DB_PREFIX."email_notifications WHERE id = 1", ARRAY_A );
-if ( $eventsManagementSettings ) {
+if ( $eventsManagementSettings && $emailNotifications ) {
$eventsManagementSettings = array_merge( $eventsManagementSettings, $emailNotifications );
}