package union import (	"bytes"	"fmt") // The Errors type wraps a slice of errorstype Errors []error // Map returns a copy of the error slice with all its errors modified// according to the mapping function. If mapping returns nil,// the error is dropped from the error slice with no replacement.func (e Errors) Map(mapping func(error) error) Errors {	s := make([]error, len(e))	i := 0	for _, err := range e {		nerr := mapping(err)		if nerr == nil {			continue		}		s[i] = nerr		i++	}	return Errors(s[:i])} // FilterNil returns the Errors without nilfunc (e Errors) FilterNil() Errors {	ne := e.Map(func(err error) error {		return err	})	return ne} // Err returns an error interface that filtered nil,// or nil if no non-nil Error is presented.func (e Errors) Err() error {	ne := e.FilterNil()	if len(ne) == 0 {		return nil	}	return ne} // Error returns a concatenated string of the contained errorsfunc (e Errors) Error() string {	var buf bytes.Buffer 	if len(e) == 0 {		buf.WriteString("no error")	}	if len(e) == 1 {		buf.WriteString("1 error: ")	} else {		fmt.Fprintf(&buf, "%d errors: ", len(e))	} 	for i, err := range e {		if i != 0 {			buf.WriteString("; ")		} 		buf.WriteString(err.Error())	} 	return buf.String()}