How do I fix InvalidCastException?

In my attached Job/Applicant matching application I'm all of a sudden getting thei "Operator '=' is not defined for type 'DBNull' and type 'Integer' (line 177).
It happens when I select a row in the ApplicantsDataGridView (top one) and select a row in the JobTitlesDataGridView (bottom one) then click the Assign Job Title button (btnUpdatePosition)

    Function getJobTitleIndex(ByVal ID As Integer) As Integer
        For Each row As DataGridViewRow In Me.JobTitlesDataGridView.Rows
            If row.Cells(19).Value = ID Then
                Return row.Index
            End If
        Next
    End Function

    Function getApplicantIndex(ByVal ID As Integer) As Integer
        For Each row As DataGridViewRow In Me.ApplicantsDataGridView.Rows
            If row.Cells(5).Value = ID Then    ' <----- ####  The Error happens here ####
                Return row.Index
            End If
        Next
    End Function

Private Sub btnUpdatePosition_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnUpdatePosition.Click
        ' ' -=== Assign Worksite to Youth Button ===-
        ' 'Call the function to get the currently selected row of JobTitlesDataGridView
        'Dim myPreviousValue As Long = Me.JobTitlesDataGridView.SelectedRows.Item(0).Cells(19).Value
        ' Stores the current row number
        ' Check if there's any selected row
        'If Not Me.JobTitlesDataGridView.SelectedRows Is Nothing Then 'CurrentRow Is Nothing Then
        If Me.JobTitlesDataGridView.SelectedRows.Count > 0 Then
            'If Not Me.ApplicantsDataGridView.SelectedRows Is Nothing Then 'CurrentRow Is Nothing Then
            If Me.ApplicantsDataGridView.SelectedRows.Count > 0 Then

                Dim SelectedID As Integer = Me.JobTitlesDataGridView.CurrentRow.Cells(19).Value
                Dim SelectedID2 As Integer = Me.ApplicantsDataGridView.CurrentRow.Cells(5).Value

                Me.Cursor = Cursors.WaitCursor
                Call UpdateAll()
                Call RefreshAll()
                Me.Cursor = Cursors.Default

                ' Set the old position
                Dim DGVindex As Integer = getJobTitleIndex(SelectedID)
                Me.JobTitlesDataGridView.ClearSelection()
                Me.JobTitlesDataGridView.Rows(DGVindex).Selected = True
                Me.JobTitlesDataGridView.FirstDisplayedScrollingRowIndex = DGVindex

                Dim DGVindex2 As Integer = getApplicantIndex(SelectedID2)
                Me.ApplicantsDataGridView.ClearSelection()
                Me.ApplicantsDataGridView.Rows(DGVindex2).Selected = True
                Me.ApplicantsDataGridView.FirstDisplayedScrollingRowIndex = DGVindex2

                Me.JobTitlesDataGridView.ClearSelection()
                Me.ApplicantsDataGridView.ClearSelection()

            Else
                Exit Sub
            End If
        End If
        ''Restore the previously selected row after an update.
        'Dim myRowIndex As Integer = getDGindex(myPreviousValue)
        'Me.JobTitlesDataGridView.Rows(myRowIndex).Selected = True
        'Me.JobTitlesDataGridView.FirstDisplayedScrollingRowIndex = myRowIndex

        ''Maybe put here UpdateTotals() then RefreshAll()  'Note for 20090312
        ''UpdateTotals() is already called in UpdateAll()
    End Sub

I jut don't know enough to know how to fix it.  Assistance appreciated.

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'There was no problem with this one:
 
    Function getJobTitleIndex(ByVal ID As Integer) As Integer
        For Each row As DataGridViewRow In Me.JobTitlesDataGridView.Rows
            If row.Cells(19).Value = ID Then
                Return row.Index
            End If
        Next
    End Function
 
'The error happens on this one:
 
    Function getApplicantIndex(ByVal ID As Integer) As Integer
        For Each row As DataGridViewRow In Me.ApplicantsDataGridView.Rows
            If row.Cells(5).Value = ID Then
                Return row.Index
            End If
        Next
    End Function