Fixed #15082

CHANGELOG.md

@@ -12,6 +12,7 @@
 - Fixed a bug where field layout designers weren’t displaying native fields in the library pane when a tab was removed that contained them. ([#15064](https://github.com/craftcms/cms/issues/15064))
 - Fixed a bug where recent textual changes could be lost when creating a new inline-editable Matrix block, if the block was created before the autosave had a chance to initiate. ([#15069](https://github.com/craftcms/cms/issues/15069))
 - Fixed a bug where the `users/create` command would fail without explaining why, when the maximum number of users had already been reached.
+- Fixed a validation error that could occur when saving an entry on Craft Solo. ([#15082](https://github.com/craftcms/cms/issues/15082))
 
 ## 5.1.7 - 2024-05-25
 

src/elements/Entry.php

@@ -2201,8 +2201,15 @@ private function _userPostDate(): ?DateTime
      */
     public function beforeValidate(): bool
     {
-        if (!isset($this->_authorIds) && !isset($this->fieldId) && $this->getSection()->type !== Section::TYPE_SINGLE) {
-            $this->setAuthor(Craft::$app->getUser()->getIdentity());
+        if (
+            (!isset($this->_authorIds) || empty($this->_authorIds)) &&
+            !isset($this->fieldId) &&
+            $this->getSection()->type !== Section::TYPE_SINGLE
+        ) {
+            $user = Craft::$app->getUser()->getIdentity();
+            if ($user) {
+                $this->setAuthor($user);
+            }
         }
 
         if (