Make sure Period::toString() handles case when child period returns array and add a unit test. (#13762)

* Make sure Period::toString() always returns array of strings and add a unit test.

* Ensure backwards compatible.

* docblock tweak

* Fix tests.

1 files changed, 7 insertions, 2 deletions

diff --git a/core/Period.php b/core/Period.php
index 8cd849ba41..c9b0c04900 100644
--- a/core/Period.php
+++ b/core/Period.php
@@ -264,7 +264,7 @@ abstract class Period
      * Returns a list of strings representing the current period.
      *
      * @param string $format The format of each individual day.
-     * @return array An array of string dates that this period consists of.
+     * @return array|string An array of string dates that this period consists of.
      */
     public function toString($format = "Y-m-d")
     {
@@ -272,7 +272,12 @@ abstract class Period
 
         $dateString = array();
         foreach ($this->subperiods as $period) {
-            $dateString[] = $period->toString($format);
+            $childPeriodStr = $period->toString($format);
+            if (is_array($childPeriodStr)) {
+                $childPeriodStr = implode(",", $childPeriodStr);
+            }
+
+            $dateString[] = $childPeriodStr;
         }
 
         return $dateString;