entuser.User_Name.Value = 'entuser.User_Name.Value' threw an exception of type 'System.Data.SqlTypes.SqlNullValueException' – Asp.net

currently i am working a one project and i got this type of error.
i excuted the procedure and in debugging mode prcedure pass the data to entity file but when i go back to aspx page so that time i got this null exception.
how can i resolve.
any one help me?.

UserDAL file

this is a prcedure

public UserENT PR_IP_User_LoginUser(SqlInt32 UserID)
{
   using (SqlConnection objconn = new SqlConnection(ConnectionString))
   {
      objconn.Open();
      using (SqlCommand objcmd = objconn.CreateCommand())
      {
         try
         {
            #region Prepaed Command
            objcmd.CommandType = CommandType.StoredProcedure;
            objcmd.CommandText = "PR_IP_User_LoginUser";
            objcmd.Parameters.AddWithValue("@UserID", UserID);
            #endregion

             UserENT entuser = new UserENT();
             #region Read and set controls
             using (SqlDataReader objSDR = objcmd.ExecuteReader())
             {
                while (objSDR.Read())
                {
                   if (!objSDR["User_Name"].Equals(DBNull.Value))
                   {
                      entuser.User_Name = Convert.ToString(objSDR["User_Name"].ToString().Trim());
                   }

                   if (!objSDR["Password"].Equals(DBNull.Value))
                   {
                      entuser.Password = Convert.ToString(objSDR["Password"].ToString().Trim());
                   }

                   if (!objSDR["User_ID"].Equals(DBNull.Value))
                   {
                        entuser.User_ID = Convert.ToInt32(objSDR["User_ID"]);
                   }

                   if (!objSDR["ContactNo"].Equals(DBNull.Value))
                   {
                        entuser.ContactNo = Convert.ToString(objSDR["ContactNo"]);
                   }

                   if (!objSDR["Email_ID"].Equals(DBNull.Value))
                   {
                       entuser.Email_ID = Convert.ToString(objSDR["Email_ID"]);
                   }

                   if (!objSDR["Is_Admin"].Equals(DBNull.Value))
                   {
                       entuser.Is_Admin = Convert.ToBoolean(objSDR["Is_Admin"]);
                   }

              }

           return entuser;
        }
        #endregion

        }
        catch (Exception e)
        {
            Message = e.InnerException.Message;
            return null;
         }
         finally
         {
             objconn.Close();
         }
      }
    }
 }
        #endregion

on client side or can say aspx page

on button click event

protected void btnLogin_Click(object sender, EventArgs e)
{ 
     #region Server Side Validation
    String strerr = "";

    if (txtusername.Text.Trim() == "")
    {
        strerr += "Enter UserName";
    }

    if (txtpassword.Text.Trim() == "")
    {
        strerr += "Enter Password";
    }

    if (strerr != "")
    {
        lblMessage.EnableViewState = true;
        lblMessage.Text = strerr;
    }
     #endregion

     #region Gather Data

     SqlString Username, userpass;

     if (txtusername.Text.Trim() != "")
     {
        Username = txtusername.Text.Trim();
     }

     if (txtpassword.Text.Trim() != "")
     {
        userpass = txtusername.Text.Trim();
     }

      #endregion

      UserBAL baluser = new UserBAL();
      UserENT entuser = new UserENT();
      SqlInt32 UserID_Res;
      SqlString User_name_res, User_Password_res;
      SqlInt32 userid = Convert.ToInt32(txtuserid.Text.Trim());
      if (Request.QueryString["User_ID"] == null)
      {
          if (baluser.Login(userid) != null)
          {
              User_name_res = entuser.User_Name.Value.ToString().Trim();
              UserID_Res = Convert.ToInt32(entuser.User_ID.Value);
              User_Password_res = entuser.Password.Value.ToString().Trim();

               if (User_name_res == txtusername.Text.Trim() || User_Password_res == txtpassword.Text.Trim())
               {
                  Response.Redirect("AddSubject.aspx");
               }
               else
               {
                   Response.Redirect("AddTopic.aspx");
               }
           }
       }
        
    #endregion