Scanning sql.NullInt64 value fails when row is created via FromCSVString

[craigfitzpatrick]

When you create a row with a null value using the sqlmock.FromCSVString function, sql.Rows.Scan fails with a conversion error while scanning that value. The following test:

func TestNullScanFromCSV(t *testing.T) {

	const query string = "select nullable from TableWithNulls"

	db, mock, err := New()
	if err != nil {
		t.Fatalf("an error '%s' was not expected when opening a stub database connection", err)
	}
	defer db.Close()

	rs := NewRows([]string{"nullable"}).AddRow(1).AddRow(nil).FromCSVString("null")

	mock.ExpectQuery(query).WillReturnRows(rs)

	var expectedResults = []sql.NullInt64{
		{Valid: true, Int64: 1},
		{Valid: false, Int64: 0},
		{Valid: false, Int64: 0},
	}

	rows, err := db.Query(query)
	if err != nil {
		t.Fatalf("an error '%s' was not expected when querying a stub database connection", err)
	}
	defer rows.Close()

	var actualResults []sql.NullInt64
	for rows.Next() {
		var ni sql.NullInt64
		if err = rows.Scan(&ni); err != nil {
			t.Fatalf("an error '%s' was not expected while scanning row from mocked recordset", err)
		}
		actualResults = append(actualResults, ni)
	}

	if len(expectedResults) != len(actualResults) {
		t.Fatalf("unexpected row count: wanted %d, got %d", len(expectedResults), len(actualResults))
	}

	for i, v := range actualResults {
		if v != expectedResults[i] {
			t.Fatalf("unexpected value in row %d: wanted %v, got %v", i, expectedResults[i], v)
		}
	}

	if err = mock.ExpectationsWereMet(); err != nil {
		t.Fatal(err)
	}
}

Demonstrates the failure:

$ go test go-sqlmock -run ^TestNullScanFromCSV$
--- FAIL: TestNullScanFromCSV (0.00s)
	rows_test.go:349: an error 'sql: Scan error on column index 0: converting driver.Value type []uint8 ("") to a int64: invalid syntax' was not expected while scanning row from mocked recordset
FAIL
FAIL	go-sqlmock	0.002s

I believe that the fix is a simple as changing the return type of sqlmock.CSVColumnParser and have submitted pull request #141 with that change.

[craigfitzpatrick]

As per l3pp4rd's suggestion, I have reopened my pull request against the v2 branch (see pull request #142), because the change I suggested is backwards incompatible.