VB005 写入数据库错误 怎么解决

无法将 NULL 值插入列 'chexing'，表 'fty.dbo.车型表'；该列不允许空值。INSERT 失败。
语句已终止。
 表为：车型表 列名chexing（主键）  chepaihao  explain
  
        Dim conn As New SqlConnection("Data Source=FTY;Initial Catalog=fty;Integrated Security=True ")
        Dim str As String
        str = "insert into 车型表(chepaihao)   values( 'textbox1.text' )"
        Dim comm As New SqlCommand(str, conn)
        conn.Open()
        comm.ExecuteNonQuery()
        conn.Close()