Fix #5: skip unexported fields, allow nil values

Thanks @RangelReale for bringing that issue up and proposing a fix!

sheriff.go

@@ -79,6 +79,10 @@ func Marshal(options *Options, data interface{}) (interface{}, error) {
 		if jsonOpts.Contains("omitempty") && isEmptyValue(val) {
 			continue
 		}
+		// skip unexported fields
+		if !val.IsValid() || !val.CanInterface() {
+			continue
+		}
 
 		// if there is an anonymous field which is a struct
 		// we want the childs exposed at the toplevel to be
@@ -144,6 +148,10 @@ func Marshal(options *Options, data interface{}) (interface{}, error) {
 //
 // There is support for types implementing the Marshaller interface, arbitrary structs, slices, maps and base types.
 func marshalValue(options *Options, v reflect.Value) (interface{}, error) {
+	// return nil on nil pointer struct fields
+	if !v.IsValid() || !v.CanInterface() {
+		return nil, nil
+	}
 	val := v.Interface()
 
 	if marshaller, ok := val.(Marshaller); ok {

sheriff_test.go

@@ -464,3 +464,35 @@ func TestMarshal_EmbeddedFieldEmpty(t *testing.T) {
 
 	assert.Equal(t, string(expected), string(actual))
 }
+
+type TestInlineStruct struct {
+	tableName        struct{ Test string } `json:"-"`
+	tableNameWithTag struct{ Test string } `json:"foo"`
+
+	Field  string  `json:"field"`
+	Field2 *string `json:"field2"`
+}
+
+func TestMarshal_InlineStruct(t *testing.T) {
+	v := TestInlineStruct{
+		tableName:        struct{ Test string }{"test"},
+		tableNameWithTag: struct{ Test string }{"testWithTag"},
+		Field:            "World",
+		Field2:           nil,
+	}
+	o := &Options{}
+
+	actualMap, err := Marshal(o, v)
+	assert.NoError(t, err)
+
+	actual, err := json.Marshal(actualMap)
+	assert.NoError(t, err)
+
+	expected, err := json.Marshal(map[string]interface{}{
+		"field":  "World",
+		"field2": nil,
+	})
+	assert.NoError(t, err)
+
+	assert.Equal(t, string(expected), string(actual))
+}