diff --git a/reportbuilder/classes/local/aggregation/base.php b/reportbuilder/classes/local/aggregation/base.php
index 19d5686a0a2..bc2a5e20fdb 100644
--- a/reportbuilder/classes/local/aggregation/base.php
+++ b/reportbuilder/classes/local/aggregation/base.php
@@ -81,9 +81,14 @@ abstract class base {
      *
      * @param string[] $sqlfields
      * @param string $delimeter
+     * @param string $coalescechar
      * @return string
      */
-    final protected static function get_column_fields_concat(array $sqlfields, string $delimeter = ','): string {
+    final protected static function get_column_fields_concat(
+        array $sqlfields,
+        string $delimeter = ',',
+        string $coalescechar = ' '
+    ): string {
         global $DB;
 
         // We need to ensure all values are char.
@@ -95,8 +100,8 @@ abstract class base {
                 $sqlfield = $DB->sql_cast_to_char($sqlfield);
             }
 
-            // Coalesce all the SQL fields, to remove all nulls.
-            $concatfields[] = "COALESCE({$sqlfield}, ' ')";
+            // Coalesce all the SQL fields. Ensure cross-DB compatibility, and that we always get string data back.
+            $concatfields[] = "COALESCE({$sqlfield}, '{$coalescechar}')";
             $concatfields[] = "'{$delimeter}'";
         }
 
diff --git a/reportbuilder/classes/local/aggregation/groupconcat.php b/reportbuilder/classes/local/aggregation/groupconcat.php
index e3572a9eba7..4cd07b47aba 100644
--- a/reportbuilder/classes/local/aggregation/groupconcat.php
+++ b/reportbuilder/classes/local/aggregation/groupconcat.php
@@ -34,6 +34,9 @@ class groupconcat extends base {
     /** @var string Character to use as a delimeter between column fields */
     protected const COLUMN_FIELD_DELIMETER = '<|>';
 
+    /** @var string Character to use a null coalesce value */
+    protected const COLUMN_NULL_COALESCE = '<^>';
+
     /** @var string Character to use as a delimeter between field values */
     protected const FIELD_VALUE_DELIMETER = '<,>';
 
@@ -79,7 +82,7 @@ class groupconcat extends base {
             return parent::get_column_field_sql($sqlfields);
         }
 
-        return self::get_column_fields_concat($sqlfields, self::COLUMN_FIELD_DELIMETER);
+        return self::get_column_fields_concat($sqlfields, self::COLUMN_FIELD_DELIMETER, self::COLUMN_NULL_COALESCE);
     }
 
     /**
@@ -124,7 +127,11 @@ class groupconcat extends base {
                 continue;
             }
 
-            $originalvalues = array_combine($valuenames, $valuedata);
+            // Re-construct original values, also ensuring any nulls contained within are restored.
+            $originalvalues = array_map(static function(string $value): ?string {
+                return $value === self::COLUMN_NULL_COALESCE ? null : $value;
+            }, array_combine($valuenames, $valuedata));
+
             $originalvalue = column::get_default_value($originalvalues, $columntype);
 
             // Once we've re-constructed each value, we can apply callbacks to it.
diff --git a/reportbuilder/tests/local/aggregation/groupconcat_test.php b/reportbuilder/tests/local/aggregation/groupconcat_test.php
index e162d09cf81..c339e626c16 100644
--- a/reportbuilder/tests/local/aggregation/groupconcat_test.php
+++ b/reportbuilder/tests/local/aggregation/groupconcat_test.php
@@ -18,6 +18,8 @@ declare(strict_types=1);
 
 namespace core_reportbuilder\local\aggregation;
 
+use core_badges_generator;
+use core_badges\reportbuilder\datasource\badges;
 use core_reportbuilder_testcase;
 use core_reportbuilder_generator;
 use core_user\reportbuilder\datasource\users;
@@ -141,4 +143,53 @@ class groupconcat_test extends core_reportbuilder_testcase {
             ],
         ], $content);
     }
+
+    /**
+     * Test aggregation when applied to column with callback that expects/handles null values
+     */
+    public function test_datasource_aggregate_column_callback_with_null(): void {
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        $userone = $this->getDataGenerator()->create_user(['description' => 'First user']);
+        $usertwo = $this->getDataGenerator()->create_user(['description' => 'Second user']);
+
+        /** @var core_badges_generator $generator */
+        $generator = $this->getDataGenerator()->get_plugin_generator('core_badges');
+
+        // Create course badge, issue to both users.
+        $badgeone = $generator->create_badge(['name' => 'First badge']);
+        $badgeone->issue($userone->id, true);
+        $badgeone->issue($usertwo->id, true);
+
+        // Create second badge, without issuing to anyone.
+        $badgetwo = $generator->create_badge(['name' => 'Second badge']);
+
+        /** @var core_reportbuilder_generator $generator */
+        $generator = $this->getDataGenerator()->get_plugin_generator('core_reportbuilder');
+        $report = $generator->create_report(['name' => 'Badges', 'source' => badges::class, 'default' => 0]);
+
+        // First column, sorted.
+        $generator->create_column(['reportid' => $report->get('id'), 'uniqueidentifier' => 'badge:name'])
+            ->set('sortenabled', true)
+            ->update();
+
+        // This is the column we'll aggregate.
+        $generator->create_column(['reportid' => $report->get('id'), 'uniqueidentifier' => 'user:description'])
+            ->set('aggregation', groupconcat::get_class_name())
+            ->update();
+
+        // Assert description column was aggregated, with callbacks accounting for null values.
+        $content = $this->get_custom_report_content($report->get('id'));
+        $this->assertEquals([
+            [
+                'c0_name' => $badgeone->name,
+                'c1_description' => "{$userone->description}, {$usertwo->description}",
+            ],
+            [
+                'c0_name' => $badgetwo->name,
+                'c1_description' => '',
+            ],
+        ], $content);
+    }
 }