Failed to add pass error about passkit HOT 7 OPEN

c := passkit.NewBoardingPass(passkit.TransitTypeAir)

// Utility functions for adding fields to a pass
c.AddHeaderField(passkit.Field{
    Key: "your_head_key",
    Label: "your_displayable_head_label",
    Value:"value",
})
c.AddPrimaryFields(passkit.Field{
    Key: "your_prim_key",
    Label: "your_displayable_prim_label",
    Value:"value",
})
c.AddSecondaryFields(passkit.Field{
    Key: "your_sec_key",
    Label: "your_displayable_sec_label",
    Value:"value",
})
c.AddAuxiliaryFields(passkit.Field{
    Key: "your_aux_key",
    Label: "your_displayable_aux_label",
    Value:"value",
})
c.AddBackFields(passkit.Field{
    Key: "your_back_key",
    Label: "your_displayable_back_label",
    Value:"value",
})

pass := passkit.Pass{
    FormatVersion:       1,
    TeamIdentifier:      "TEAMID",
    PassTypeIdentifier:  "pass.type.id",
    AuthenticationToken: "123141lkjdasj12314",
    OrganizationName:    "Your Organization",
    SerialNumber:        "1234",
    Description:         "test",
    BoardingPass:         c,
    Barcodes: []passkit.Barcode{
        {
            Format:          passkit.BarcodeFormatPDF417,
            Message:         "1312312312312312312312312312",
            MessageEncoding: "utf-8",
        },
    },
}