Generator haseł MySQL i błąd NotImplementedException

Imports System
Imports System.Text
Imports System.Security.Cryptography
Public Class Form1
    Public Function Generatorhash(ByVal str As String) As String
        Dim get_h = New SHA1Managed().ComputeHash(New SHA1Managed().ComputeHash(Encoding.UTF8.GetBytes(a)))
        Dim pc_h As New StringBuilder(get_h.Length)
        For Each pa_p As Byte In get_h
            pc_h.Append(pa_p.ToString("X2"))
        Next
        Return "*" & pc_h.ToString()
    End Function
    Private Sub CheckBox1_CheckedChanged(ByVal sender As Object, ByVal e As EventArgs)
        If CheckBox1.Checked Then
            TextBox2.UseSystemPasswordChar = True
        Else
            TextBox2.UseSystemPasswordChar = False
        End If
    End Sub
    Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
        TextBox1.Text = Generatorhash(TextBox2.Text)
        If TextBox2.Text.Length = Nothing Then
            TextBox1.Text = ""
            MessageBox.Show("Wpisz hasło do wygenerowania", "Pustę pole", MessageBoxButtons.OK, MessageBoxIcon.Error, MessageBoxDefaultButton.Button1)
        Else
            Button1.Enabled = False : TextBox2.Enabled = False : CheckBox1.Enabled = False
        End If
    End Sub
    Private Sub Button2_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button2.Click
        Button1.Enabled = True : TextBox2.Enabled = True : TextBox1.Text = "" : TextBox2.Text = "" : CheckBox1.Enabled = True
    End Sub
    Private Function a() As Char()
        Throw New NotImplementedException
    End Function
End Class

 Private Function a() As Char()
        Throw New NotImplementedException
    End Function

A first chance exeption of type 'System.NotImplementedException' occurred in WindowsApplication.exe

 Private Function a() As Char()
        Throw New NotImplementedException
    End Function

rivate Function a() As Char()
    Throw New NotImplementedException
End Function