Improve handling of <nil> Params

Fixes #8825

common/maps/maps.go

@@ -17,6 +17,8 @@ import (
 	"fmt"
 	"strings"
 
+	"github.com/gohugoio/hugo/common/types"
+
 	"github.com/gobwas/glob"
 	"github.com/spf13/cast"
 )
@@ -39,8 +41,12 @@ func ToStringMapE(in interface{}) (map[string]interface{}, error) {
 }
 
 // ToParamsAndPrepare converts in to Params and prepares it for use.
+// If in is nil, an empty map is returned.
 // See PrepareParams.
 func ToParamsAndPrepare(in interface{}) (Params, bool) {
+	if types.IsNil(in) {
+		return Params{}, true
+	}
 	m, err := ToStringMapE(in)
 	if err != nil {
 		return nil, false

common/maps/maps_test.go

@@ -114,6 +114,16 @@ func TestToSliceStringMap(t *testing.T) {
 	}
 }
 
+func TestToParamsAndPrepare(t *testing.T) {
+	c := qt.New(t)
+	_, ok := ToParamsAndPrepare(map[string]interface{}{"A": "av"})
+	c.Assert(ok, qt.IsTrue)
+
+	params, ok := ToParamsAndPrepare(nil)
+	c.Assert(ok, qt.IsTrue)
+	c.Assert(params, qt.DeepEquals, Params{})
+}
+
 func TestRenameKeys(t *testing.T) {
 	c := qt.New(t)