use of unassigned local variable 'dt'

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;
using System.Windows.Forms;
using System.Data;

namespace DAL
{
    public class dbHelper
    {
        SqlConnection SQLConn;
        string connectionstring;
        SqlDataAdapter da;
        public void openconnection()
        {
            connectionstring = "Server=GITTWO-PC\\SQL2008R2;Database=emp;User Id=accpac;Password=super1;";
            try
            {
                SQLConn = new SqlConnection(connectionstring);
                SQLConn.Open();
            }
            catch(Exception ex)
            {
                MessageBox.Show(" Error Connecting to database! - " + ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }

        public void closeconnection()
        {
            SQLConn.Close();
        }
            
        public DataTable getdt(string query)
        {
            openconnection();
            da = new SqlDataAdapter(query, SQLConn);
            DataTable dt;
            da.Fill(dt);
            closeconnection();
            return dt;
        }
    
        public Boolean executequery(String query)
        {
            openconnection();
            SqlCommand com =new SqlCommand(query, SQLConn);
            com.ExecuteNonQuery();
            closeconnection();
            return true;
        }
    }
}