1 files changed, 6 insertions, 2 deletions

diff --git a/errors.go b/errors.go
index 3404c7e..5576ecd 100644
--- a/errors.go
+++ b/errors.go
@@ -1,11 +1,11 @@
-// Copyright 2016 - 2019 The excelize Authors. All rights reserved. Use of
+// Copyright 2016 - 2020 The excelize Authors. All rights reserved. Use of
 // this source code is governed by a BSD-style license that can be found in
 // the LICENSE file.
 //
 // Package excelize providing a set of functions that allow you to write to
 // and read from XLSX files. Support reads and writes XLSX file generated by
 // Microsoft Excel™ 2007 and later. Support save file without losing original
-// charts of XLSX. This library needs Go version 1.8 or later.
+// charts of XLSX. This library needs Go version 1.10 or later.
 
 package excelize
 
@@ -22,3 +22,7 @@ func newInvalidRowNumberError(row int) error {
 func newInvalidCellNameError(cell string) error {
 	return fmt.Errorf("invalid cell name %q", cell)
 }
+
+func newInvalidExcelDateError(dateValue float64) error {
+	return fmt.Errorf("invalid date value %f, negative values are not supported supported", dateValue)
+}