Fix issue 55 (#56)

* test

* fix

---------

Co-authored-by: Aleksey Mikhaylov <mikhailov.av@exmo.com>

Author: mikhalytch

bindform.go

@@ -288,7 +288,12 @@ func bindAdditionalProperties(additionalProperties reflect.Value, parentStruct r
 
 func marshalFormImpl(v reflect.Value, result url.Values, name string) {
 	switch v.Kind() {
-	case reflect.Interface, reflect.Ptr:
+	case reflect.Ptr:
+		if v.IsNil() {
+			break
+		}
+		fallthrough
+	case reflect.Interface:
 		marshalFormImpl(v.Elem(), result, name)
 	case reflect.Slice:
 		for i := 0; i < v.Len(); i++ {

bindform_test.go

@@ -133,6 +133,7 @@ func TestMarshalForm(t *testing.T) {
 		StructSlice     []testSubStruct  `json:"struct_slice,omitempty"`
 		OptInt          *int             `json:"opt_int,omitempty"`
 		OptBool         *bool            `json:"opt_bool,omitempty"`
+		OptBoolNullable *bool            `json:"opt_bool_nullable"`
 		OptString       *string          `json:"opt_string,omitempty"`
 		OptStruct       *testSubStruct   `json:"opt_struct,omitempty"`
 		OptStructSlice  *[]testSubStruct `json:"opt_struct_slice,omitempty"`
@@ -151,6 +152,7 @@ func TestMarshalForm(t *testing.T) {
 		},
 		"opt_int=456":    {OptInt: func(v int) *int { return &v }(456)},
 		"opt_bool=true":  {OptBool: func(v bool) *bool { return &v }(true)},
+		"":               {OptBoolNullable: nil},
 		"opt_string=def": {OptString: func(v string) *string { return &v }("def")},
 		"opt_struct[int]=456&opt_struct[string]=def": {OptStruct: &testSubStruct{Int: 456, String: "def"}},
 		"opt_struct_slice[0][int]=123&opt_struct_slice[0][string]=abc&opt_struct_slice[1][int]=456&opt_struct_slice[1][string]=def": {