conversion problem string to GUID

[Sandy]

I am trying to convert a string into a uniqueidentifier by using the following code

Dim contrID = Request.Params("oId"
Dim sqlID As SqlGuid = SqlGuid.Parse(contrID

I am then putting sqlID into my SQL WHERE clause so it only pulls that record. I've double checked that the record I'm trying to pull is in the database. I am getting the error below. I don't understand what is causing it, Any Help is appreciated!!!!!!

ArgumentNull_String Parameter name: g
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentNullException: ArgumentNull_String Parameter name:

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[ArgumentNullException: ArgumentNull_Strin
Parameter name: g
System.Guid..ctor(String g) +341
System.Data.SqlTypes.SqlGuid..ctor(String s) +3
System.Data.SqlTypes.SqlGuid.Parse(String s) +1
Contract_Contact.grid_data.GetDataset(String sortcolumn, ColumnSortDirection sortdirection
Contract_Contact.grid_data.Page_Load(Object sender, EventArgs e
System.Web.UI.Control.OnLoad(EventArgs e) +6
System.Web.UI.Control.LoadRecursive() +3
System.Web.UI.Page.ProcessRequestMain() +73