SQL request for C# not received

[esther]

I write to SQL the following request:

SELECT *
FROM Materials,
     PARAMETERS,
     [Values],
     Suppliers,
     Sensors
WHERE [Values].MaterialId = Materials.Id
  AND [Values].SensorId = Sensors.Id
  AND Materials.SupplierId = Suppliers.Id
  AND PARAMETERS.Id = Sensors.ParameterId
  AND MaterialName='Зерно'

Everything works correctly, That's what I'm trying to write on C#:

_comandText = "SELECT * FROM Materials,Parameters,[Values],Suppliers,Sensors WHERE [Values].MaterialId = Materials.Id AND [Values].SensorId = Sensors.Id AND Materials.SupplierId = Suppliers.Id AND Parameters.Id = Sensors.ParameterId";
...
_comandText += " AND MaterialName='" + m.MaterialName + "'";
// _comandText на 100% совпадает с запросом на SQL, я брал его(запрос для SQL) прямо отсюда во время дебага проги
...
private DataTable _table;
...
_table = RaportGateway.Instance.GetRaport(_comandText);
...
 public DataTable GetRaport(string commandText)
        {
            cmd = new SqlCommand(commandText, Connection);
            _adapter = new SqlDataAdapter(cmd);
            try
            {
                _adapter.Fill(_table);
            return _table;
        }
        catch (Exception ex)
        { // тут ловится Value cannot be null.Parameter name: dataTable, в _table соответственно null
            MessageBox.Show(ex.Message);
        }
        finally
        {
            if (Connection.State == ConnectionState.Open)
                Connection.Close();
        }
    }

Why would that be?

[jules]

private DataTable _table = new DataTable();