Cast from type 'DBNull' to type 'String' is not valid

How to modify code to remove error: Cast from type 'DBNull' to type 'String' is not valid valid when cell is empty?

Private Sub TblWorkorderDataGridView_CellEndEdit(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles TblWorkorderDataGridView.CellEndEdit
        Dim strUpperValue As String
        'Apply to certain columns        
        Select Case e.ColumnIndex
            Case 10 
                strUpperValue = TblWorkorderDataGridView.CurrentCell.Value
                TblWorkorderDataGridView.CurrentCell.Value = strUpperValue.ToUpper
        End Select

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dave_skyConnect With a Mentor Author Commented:
I found some code that works fine:

 Private Sub TblWorkorderDataGridView_CellEndEdit(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles TblWorkorderDataGridView.CellEndEdit

        If e.ColumnIndex = 10 Then
            TblWorkorderDataGridView.Rows(e.RowIndex).Cells(e.ColumnIndex).Value = TblWorkorderDataGridView.Rows(e.RowIndex).Cells(e.ColumnIndex).Value.ToString().ToUpper()
        End If

    End Sub

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Thanks everyone for your efforts!
Use an if statement to check if the cell value is null before assigning it to the string
if (Not (TblWorkorderDataGridView.CurrentCell.Value is Nothing or TblWorkorderDataGridView.CurrentCell.Value = DBNull.value))
  strUpperValue = TblWorkorderDataGridView.CurrentCell.Value

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Here's another way to code it ...
strUpperValue = ""
If TblWorkorderDataGridView.CurrentCell.Value IsNot Nothing AndAlso TblWorkorderDataGridView.CurrentCell.Value.Length > 0 Then
    strUpperValue = TblWorkorderDataGridView.CurrentCell.Value 
End If

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I'm using following function:
        Public Shared Function GetDBString(ByVal o As Object, Optional ByVal strDBNull As String = "") As String
            If o Is Nothing Then Return strDBNull
            If IsDBNull(o) Then Return strDBNull Else Return o.ToString
        End Function

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Now you can use from anywhere:
Dim x as String=GetDBString(TblWorkorderDataGridView.CurrentCell.Value)
If x="" Then
   MsgBox("Null value!")
End If
dave_skyAuthor Commented:
I tried all of the code samples above and none worked.

I get the error on this line when deleting text from a databridview cell (datatype nvarchar (3):
strUpperValue = TblBasicPlumbingWorkorderDataGridView.CurrentCell.Value

Here are the error details:
System.InvalidCastException was unhandled
  Message="Conversion from type 'DBNull' to type 'String' is not valid."
       at Microsoft.VisualBasic.CompilerServices.Conversions.ToString(Object Value)
       at Plumbing.frmTrackingUPBJobs.TblWorkorderDataGridView_CellEndEdit(Object sender, DataGridViewCellEventArgs e) in C:\Documents and Settings\Dave\My Documents\Visual Studio 2005\Projects\Plumbing\Plumbing\frmTrackingUPBJobs.vb:line 68
       at System.Windows.Forms.DataGridView.OnCellEndEdit(DataGridViewCellEventArgs e)
       at System.Windows.Forms.DataGridView.EndEdit(DataGridViewDataErrorContexts context, DataGridViewValidateCellInternal validateCell, Boolean fireCellLeave, Boolean fireCellEnter, Boolean fireRowLeave, Boolean fireRowEnter, Boolean fireLeave, Boolean keepFocus, Boolean resetCurrentCell, Boolean resetAnchorCell)
       at System.Windows.Forms.DataGridView.SetCurrentCellAddressCore(Int32 columnIndex, Int32 rowIndex, Boolean setAnchorCellAddress, Boolean validateCurrentCell, Boolean throughMouseClick)
       at System.Windows.Forms.DataGridView.OnCellMouseDown(HitTestInfo hti, Boolean isShiftDown, Boolean isControlDown)
       at System.Windows.Forms.DataGridView.OnCellMouseDown(DataGridViewCellMouseEventArgs e)
       at System.Windows.Forms.DataGridView.OnMouseDown(MouseEventArgs e)
       at System.Windows.Forms.Control.WmMouseDown(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.DataGridView.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(ApplicationContext context)
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine)
       at Plumbing.My.MyApplication.Main(String[] Args) in 17d14f5c-a337-4978-8281-53493378c1071.vb:line 81
       at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()

Can someone help on this?

dave_skyAuthor Commented:
All I want to do is convert the cell value to upper case and have nothing when deleted.

If I add  a binding textbox to the form - the datagridview cell formatting works fine and deletes...
Did you try
strUpperValue = GetDBString(TblBasicPlumbingWorkorderDataGridView.CurrentCell.Value)
You just want make textbox uppercase?
    Private Sub DataGridView1_EditingControlShowing(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs) Handles DataGridView1.EditingControlShowing
        If TypeOf e.Control Is TextBox Then
            If CType(sender, DataGridView).CurrentCell.ColumnIndex = 10 Then
                CType(e.Control, TextBox).CharacterCasing = CharacterCasing.Upper
            End If
        End If
    End Sub

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dave_skyAuthor Commented:
Not textbox, but datagridview column to uppercase...

the code I have is working fine...

dave_skyAuthor Commented:
I accepted my comment as a solution because no other comments worked.
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