Why the conditional Statement for stored Procedure dosen't work properly?

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SQL-Server

SQL-Server-2008

, +

Hi.
I have designed a webform wiht asp.net4 which is for Employees.in one of my page there is Checkbox and also a Textbox.so if the user checked that checkbox ,it means he has decided (to show i have studied inside the organization), and also in the Database i have mada it boolian (0,1), in otherwise if he didn't check the Checkbox the Textbox to be available for him and can write inside , and also some Nvarchar(he has studied some where else) will be inserted in the database.

a part of the code is in below:

switch (IsAlmostafaCheckBox.Checked)
            {
                case true:
                command.Parameters.AddWithValue("@IsInOrganization", this.IsOrganizationCheckBox.Checked);
                command.Parameters.AddWithValue("@InstituteName", DBNull.Value);
                    break;
                case false:
                    command.Parameters.AddWithValue("@InstituteName", this.InstituteNameTextBox.Text);
                    command.Parameters.AddWithValue("@IsInOrganization", this.IsOrganizationCheckBox.Checked);
                    break;
            }

but the problem is that when i press the button an error occures and says that you have omitted the IsInOrganization parameter in your Stored Procedure , and can not accept the null value in the database

so because i didn't want to make the field Nullable, i tried to change the stored procedure , like this :

ALTER PROCEDURE [dbo].[Insert_GeneralPassedTerms_SP](
@CityId int,
@IsInOrganization bit,
@TermTitle nvarchar(1000),
@InstituteName nvarchar(500),
@Date Datetime ,
@Duration decimal(4,1),
@Score decimal(4,2),
@Description nvarchar(1000)
)
AS
begin 
if @InstituteName=null
begin
insert into GeneralPassedTerms(
											CityId,
											IsInOrganization,
											TermTitle,
											InstituteName,
											Date,
											Duration,
											Score,
											Description
)
	Values(
											@CityId,
											@IsInOrganization,
											@TermTitle,
											'Null',
											@Date,
											@Duration,
											@Score,
											@Description
)
End
 else
     Insert into GeneralPassedTerms(
											CityId,
											IsInOrganization,
											TermTitle,
											InstituteName,
											Date,
											Duration,
											Score,
											Description
)
   Values(
											@CityId,
											@IsInOrganization,
											@TermTitle,
											@InstituteName,
											@Date,
											@Duration,
											@Score,
											@Description
)	
  select @@IDENTITY			
end

I don't whether this procedure is correct or not ? would you please help me?