Morning Lovely Monks

I have two tables as follows: 
@Clusters = qw/    Cluster_ID INT IDENTITY(1,1) PRIMARY KEY, Cluster_N
+ame VARCHAR(50) not NULL unique, DC_ID INT not NULL CONSTRAINT Cluste
+r_2_DC FOREIGN KEY REFERENCES dbo.Data_Centers(DC_ID)/;    


@Hosts = qw/Host_ID INT IDENTITY(1,1) PRIMARY KEY, Host_Name NVARCHAR(
+50) NULL, Cluster_ID int CONSTRAINT Host_2_Cluster FOREIGN KEY REFERE
+NCES dbo.Clusters(Cluster_ID), DC_ID int not NULL CONSTRAINT Host_2_D
+C FOREIGN KEY REFERENCES dbo.Data_Centers(DC_ID)/;

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and I have the following sub that I intend to use to populate the table. 
sub sql_write
{
    my ($input, $id, $type) = @_;
    if ($type eq 'SRV')
    {
        printf "SERVER HOST: %s\n", $input->{name};    
        printf "ID DC: %s\n", $id->{DC};
        printf "Cluster ID: %s\n", $id->{Cluster};
        # insert data into Hosts table                                
+                
        $dbh->do("INSERT INTO Hosts (Host_Name,Cluster_ID,DC_ID) VALUE
+S ('$input->{name}','$id->{Cluster}','$id->{DC}')");                
            
    }
}

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I call the above sub with this command 
my $rec_id = &sql_write($host_data,$Ids,"srv")

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All hosts must belong to a data center, but in the same time not all hosts are part of a cluster!

so before I call the sub I do the following to the $Ids 
$Ids->{DC} = $dc_id;
$Ids->{Cluster} = $cluster_id;

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If do have a value for a cluster then $ids->{Cluster} will have that value, but if I don't have a value for a cluster then I don't want to insert a value to the Cluster_ID, in other words I want the field to remain as "NULL"! However no matter what I have tried since yesterday I kept getting this error! 
DBD::ODBC::db do failed: [Microsoft][ODBC SQL Server Driver][SQL Serve
+r]The INSERT statement conflicted with the FOREIGN KEY cons
raint "Host_2_Cluster". The conflict occurred in database "DEV1111", t
+able "dbo.Clusters", column 'Cluster_ID'. (SQL-23000) [er
 was 1 now 1] [state was 23000 now 01000]
[Microsoft][ODBC SQL Server Driver][SQL Server]The statement has been 
+terminated. (SQL-01000) at U:\Doccuments\test.pl line 104, <DATA> lin
+e 1.

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Could kindly an enlightened monks advise where I am going wrong or how can I insert a Null value into a field that has been declared as "NULL" in an MSSQL2008 db please? Thanks
Blackadder

In reply to How to insert a NULL value into a table!! by blackadder

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