resources/page: Make sure a map is always initialized

Fixes #13810

Author: bep

resources/page/page_matcher.go

@@ -174,6 +174,9 @@ func DecodeCascade(logger loggers.Logger, handleLegacyFormat bool, in any) (*map
 
 func mapToPageMatcherParamsConfig(m map[string]any) (PageMatcherParamsConfig, error) {
 	var pcfg PageMatcherParamsConfig
+	if pcfg.Fields == nil {
+		pcfg.Fields = make(maps.Params)
+	}
 	for k, v := range m {
 		switch strings.ToLower(k) {
 		case "_target", "target":
@@ -193,9 +196,6 @@ func mapToPageMatcherParamsConfig(m map[string]any) (PageMatcherParamsConfig, er
 				}
 			}
 		default:
-			if pcfg.Fields == nil {
-				pcfg.Fields = make(maps.Params)
-			}
 
 			pcfg.Fields[k] = v
 		}

resources/page/page_matcher_test.go

@@ -99,6 +99,7 @@ func TestPageMatcher(t *testing.T) {
 			Params: maps.Params{
 				"foo": "bar",
 			},
+			Fields: maps.Params{},
 			Target: PageMatcher{Path: "", Kind: "page", Lang: "", Environment: ""},
 		})
 	})
@@ -136,9 +137,10 @@ func TestDecodeCascadeConfig(t *testing.T) {
 	c.Assert(got.SourceStructure, qt.DeepEquals, []PageMatcherParamsConfig{
 		{
 			Params: maps.Params{"a": string("av")},
+			Fields: maps.Params{},
 			Target: PageMatcher{Kind: "page", Environment: "production"},
 		},
-		{Params: maps.Params{"b": string("bv")}, Target: PageMatcher{Kind: "page"}},
+		{Params: maps.Params{"b": string("bv")}, Fields: maps.Params{}, Target: PageMatcher{Kind: "page"}},
 	})
 
 	got, err = DecodeCascadeConfig(loggers.NewDefault(), true, nil)