Add proper error message when receiving nil in Resource transformation

Closes #6128

diff --git a/resources/transform.go b/resources/transform.go
index 35ae25ec4f7085f596c93d7ba408d6955683cc83..6a188e78922ce5e726ad08fe68f27a382d41ecdc 100644 (file)
--- a/resources/transform.go
+++ b/resources/transform.go
@@ -19,6 +19,8 @@ import (
        "strconv"
        "strings"
 
+       "github.com/pkg/errors"
+
        "github.com/gohugoio/hugo/common/collections"
        "github.com/gohugoio/hugo/common/herrors"
        "github.com/gohugoio/hugo/common/hugio"
@@ -43,6 +45,10 @@ var (
 )
 
 func (s *Spec) Transform(r resource.Resource, t ResourceTransformation) (resource.Resource, error) {
+       if r == nil {
+               return nil, errors.New("got nil Resource in transformation. Make sure you check with 'with' or 'if' when you get a resource, e.g. with resources.Get.")
+       }
+
        return &transformedResource{
                Resource:                    r,
                transformation:              t,