Circle Calculator Error

I am making a calculator to switch from radius to diameter ect... but i keep getting this error (An error occurred creating the form. See Exception.InnerException for details. The error is: Object reference not set to an instance of an object.) I am not sure what to do and sorry if this is easy, i am a beginner. here is my code

Public Class Form1
    
    Dim Radius1 As Integer = Val(TextBox2.Text / 2)
    Dim Radius2 As Integer = Val(TextBox3.Text / 3.14 / 2)
    Dim Diameter1 As Integer = Val(TextBox1.Text * 2)
    Dim Diameter2 As Integer = Val(TextBox3.Text / 3.14)
    Dim Circumference1 As Integer = 3.14159 * Val(TextBox2.Text)
    Dim Circumference2 As Integer = 3.14159 * Val(TextBox1.Text * 2 * 3.14)
    Dim Radiusbox As Integer = Val(TextBox1.Text)
    Dim Diameterbox As Integer = Val(TextBox2.Text)
    Dim Circumferencebox As Integer = (TextBox3.Text)
    Dim unit As String = TextBox4.Text


    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click


        If IsNumeric(Radiusbox) Then

        ElseIf Radiusbox = "" Then

        Else
            TextBox1.BackColor = Color.Red
            TextBox1.ForeColor = Color.White

        End If


        If IsNumeric(Diameterbox) Then
            MsgBox("good")
        ElseIf Diameterbox = "" Then
            MsgBox("goodnone")
        Else
            TextBox2.BackColor = Color.Red
            TextBox2.ForeColor = Color.White

        End If

        If IsNumeric(Circumferencebox) Then

        ElseIf Circumferencebox = "" Then

        Else
            TextBox3.BackColor = Color.Red
            TextBox3.ForeColor = Color.White

        End If


    End Sub

    Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
        TextBox2.Enabled = False
        TextBox3.Enabled = False
        TextBox1.BackColor = Color.White
        TextBox1.ForeColor = Color.Black
    End Sub

    Private Sub TextBox2_TextChanged(sender As Object, e As EventArgs) Handles TextBox2.TextChanged
        TextBox1.Enabled = False
        TextBox3.Enabled = False
        TextBox2.BackColor = Color.White
        TextBox2.ForeColor = Color.Black
    End Sub

    Private Sub TextBox3_TextChanged(sender As Object, e As EventArgs) Handles TextBox3.TextChanged
        TextBox2.Enabled = False
        TextBox1.Enabled = False
        TextBox3.BackColor = Color.White
        TextBox3.ForeColor = Color.Black
    End Sub


End Class

and yes i know im not done but i get this error anyways