Index: core/kernel/session/session.php
===================================================================
--- core/kernel/session/session.php
+++ core/kernel/session/session.php
@@ -387,9 +387,15 @@
 			$this->_autoGuessDomain(SERVER_NAME)
 		);
 
-		/** @var CookieManager $cookie_manager */
-		$cookie_manager = $this->Application->recallObject('CookieManager');
-		$encrypted_value = $cookie_manager->encryptAndTrack($name, $value);
+		// Allow auto-removal of cookies with empty value that encryption would otherwise block.
+		if ( $value === '' ) {
+			$encrypted_value = '';
+		}
+		else {
+			/** @var CookieManager $cookie_manager */
+			$cookie_manager = $this->Application->recallObject('CookieManager');
+			$encrypted_value = $cookie_manager->encryptAndTrack($name, $value);
+		}
 
 		foreach ($old_style_domains as $old_style_domain) {
 			if ($this->CookieDomain != $old_style_domain) {