diff --git a/reportbuilder/classes/local/aggregation/base.php b/reportbuilder/classes/local/aggregation/base.php
index f175133970b..3997e02bef7 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;
 
         $concatfields = [];
@@ -99,8 +104,8 @@ abstract class base {
                     break;
             }
 
-            // 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 9d7daec241e..77c27b579f4 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);
     }
 
     /**
@@ -123,7 +126,11 @@ class groupconcat extends base {
                 continue;
             }
 
-            $originalvalue = array_combine($valuenames, $valuedata);
+            // Re-construct original values, also ensuring any nulls contained within are restored.
+            $originalvalue = array_map(static function(string $value): ?string {
+                return $value === self::COLUMN_NULL_COALESCE ? null : $value;
+            }, array_combine($valuenames, $valuedata));
+
             $originalfirstvalue = reset($originalvalue);
 
             // Once we've re-constructed each value, we can apply callbacks to it.