is null for label?

hi, i have the error:
System.Web.UI.WebControls.Label' does not contain a definition for 'IsNull' and no extension method 'IsNull' accepting a first argument of type 'System.Web.UI.WebControls.Label' could be found (are you missing a using directive or an assembly reference?)
referring to:
Line 26: Label3.Text = userProfile.UserName;
Line 27:
Line 28: if (!Label2.IsNull)
Line 29: {
Line 30: Label2.Visible = true;


Can anyone help? thanks!

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