diff --git a/reportbuilder/classes/local/helpers/format.php b/reportbuilder/classes/local/helpers/format.php
index 2662cd5bee8..722856acecd 100644
--- a/reportbuilder/classes/local/helpers/format.php
+++ b/reportbuilder/classes/local/helpers/format.php
@@ -35,7 +35,7 @@ class format {
     /**
      * Returns formatted date.
      *
-     * @param int $value Unix timestamp
+     * @param int|null $value Unix timestamp
      * @param stdClass $row
      * @param string|null $format Format string for strftime
      * @return string
@@ -47,20 +47,26 @@ class format {
     /**
      * Returns yes/no string depending on the given value
      *
-     * @param bool $value
+     * @param bool|null $value
      * @return string
      */
     public static function boolean_as_text($value): string {
+        if ($value === null) {
+            return '';
+        }
         return (bool) $value ? get_string('yes') : get_string('no');
     }
 
     /**
      * Returns float value as a percentage
      *
-     * @param float $value
+     * @param float|null $value
      * @return string
      */
     public static function percent($value): string {
+        if ($value === null) {
+            return '';
+        }
         return get_string('percents', 'moodle', format_float((float) $value));
     }
 }
diff --git a/reportbuilder/classes/local/report/column.php b/reportbuilder/classes/local/report/column.php
index d0177c3e4e6..159c80caeeb 100644
--- a/reportbuilder/classes/local/report/column.php
+++ b/reportbuilder/classes/local/report/column.php
@@ -481,6 +481,7 @@ final class column {
      * The type of the $value parameter passed to the callback is determined by calling {@see set_type}, however note that
      * if the column is part of a report source and can be aggregated using one of the "Group concatenation" methods then the
      * type should be omitted if it's not string
+     * For entities that can to be left joined to a report, the first argument to their column callbacks must be nullable.
      *
      * function($value, stdClass $row[, $additionalarguments]): string
      *
@@ -649,6 +650,9 @@ final class column {
      */
     private function get_default_value(array $values) {
         $value = reset($values);
+        if ($value === null) {
+            return $value;
+        }
 
         // Ensure default value is cast to it's strict type.
         switch ($this->get_type()) {