From 869c6f4a60ea1162a5c87cce07da0f7ef9f8edaa Mon Sep 17 00:00:00 2001
From: Ryan Cramer <ryan@processwire.com>
Date: Fri, 27 Sep 2019 11:41:50 -0400
Subject: [PATCH] Fix issue processwire/processwire-issues#979

---
 wire/core/Fields.php | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/wire/core/Fields.php b/wire/core/Fields.php
index 53186a49..a18f320d 100644
--- a/wire/core/Fields.php
+++ b/wire/core/Fields.php
@@ -1062,6 +1062,9 @@ class Fields extends WireSaveableItems {
 		if($fieldtype) {
 			// ask fieldtype what is compatible
 			$fieldtypes = $fieldtype->getCompatibleFieldtypes($field);
+			if(!$fieldtypes || !$fieldtypes instanceof WireArray) {
+				$fieldtypes = $this->wire(new Fieldtypes());
+			}
 			// ensure original is present
 			$fieldtypes->prepend($fieldtype);
 		} else {