file parser: skip nil value.

pkg/config/file/raw_node.go

@@ -28,6 +28,10 @@ func decodeRaw(node *parser.Node, vData reflect.Value, filters ...string) error
 	sortedKeys := sortKeys(vData, filters)
 
 	for _, key := range sortedKeys {
+		if vData.MapIndex(key).IsNil() {
+			continue
+		}
+
 		value := reflect.ValueOf(vData.MapIndex(key).Interface())
 
 		child := &parser.Node{Name: key.String()}

pkg/config/file/raw_node_test.go

@@ -524,6 +524,20 @@ func Test_decodeRawToNode(t *testing.T) {
 				},
 			},
 		},
+		{
+			desc: "nil value",
+			data: map[string]interface{}{
+				"fii": map[interface{}]interface{}{
+					"fuu": nil,
+				},
+			},
+			expected: &parser.Node{
+				Name: "traefik",
+				Children: []*parser.Node{
+					{Name: "fii"},
+				},
+			},
+		},
 	}
 
 	for _, test := range testCases {