Incorrect syntax near ‘SET’ in asp.net c#

Question

When i updating record then this error is coming...please guide

 

below mentioned behind update button code

int id = int.Parse(lbid.Text);
string filePath = FileUpload1.PostedFile.FileName;
string customername = txtcus.Text;
string filename = Path.GetFileName(filePath);
string ext = Path.GetExtension(filename);
string contenttype = String.Empty;
switch (ext) {
 case ".doc":
  contenttype = "application/vnd.ms-word";
  break;
 case ".docx":
  contenttype = "application/vnd.ms-word";
  break;
 case ".xls":
  contenttype = "application/vnd.ms-excel";
  break;
 case ".xlsx":
  contenttype = "application/vnd.ms-excel";
  break;
 case ".jpg":
  contenttype = "image/jpg";
  break;
 case ".png":
  contenttype = "image/png";
  break;
 case ".gif":
  contenttype = "image/gif";
  break;
 case ".pdf":
  contenttype = "application/pdf";
  break;
}
Stream fs = FileUpload1.PostedFile.InputStream;
BinaryReader br = new BinaryReader(fs);
Byte[] bytes = br.ReadBytes((Int32) fs.Length);
//string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
//SqlConnection con = new SqlConnection(constr);
string query = "UPDATE Customer SET ";
SqlCommand cmd = new SqlCommand(query, con);
if (!string.IsNullOrEmpty(customername)) {
 query += "CustomerName =@CustomerName,";
 cmd.Parameters.AddWithValue("@CustomerName", customername);
}
if (!string.IsNullOrEmpty(filename)) {
 query += "Name = @Name,";
 cmd.Parameters.Add("@Name", SqlDbType.VarChar).Value = filename;
}
if (bytes.Length > 0) {
 query += "Data=@Data,";
 cmd.Parameters.Add("@Data", SqlDbType.Binary).Value = bytes;
}
if (!string.IsNullOrEmpty(contenttype)) {
 query += "ContentType=@ContentType,";
 cmd.Parameters.Add("@ContentType", SqlDbType.VarChar).Value = contenttype;
}
query = query.TrimEnd(',');
query += " WHERE CustomerId =@Id";
cmd.Parameters.AddWithValue("@Id", id);
con.Open();
cmd.ExecuteNonQuery();
con.Close();