How to insert data from TextBox to Database without watermark Text using C# in ASP.Net

hi

I use below code for put watermark for textbox:

       <asp:TextBox ID="Txtage" runat="server" CssClass="txtage" ForeColor="#443f13" onblur="WaterMark(this, event,'enter name');" onfocus="WaterMark(this, event,'enter name');" Text="enter name" onpaste="return false;"></asp:TextBox>

and insert it into database:

_cmd.Parameters.AddWithValue("@age", Txtage.Text);

now problem is that if users doesn't enter any text in textbox it will insert watermark text into database ( "enter name")

but I want if users doesn't type any text into textbox it doesn't insert any thing in databse...

best regards

neda