我需要在error（）中进行更改以解决紧急情况：运行时错误：无效的内存地址或nil指针取消引用

I have a code, but it gives

panic: runtime error: invalid memory address or nil pointer dereference [recovered] panic: runtime error: invalid memory address or nil pointer dereference

package lab2

import "fmt"
type Errors []error


func (m Errors) Error() string {


err := len(m)


if err == 0 {
    return "(0 errors)"
} else if err == 1 {
return m[0].Error()
} else if err == 2 {
return m[0].Error() + " (and 1 other error)"
} else {
return fmt.Sprintf("%s (and %d other errors)", m[0].Error(), err-1)
}   


}

TestErrorsAG: 0/16 cases passed --- PASS: TestErrorsAG (0.00s) === RUN TestErrors --- FAIL: TestErrors (0.00s) panic: runtime error: invalid memory address or nil pointer dereference [recovered] panic: runtime error: invalid memory address or nil pointer dereference [signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x511fb2]

package lab

import (
    . "io"
    "testing"
)

// String: "io: read/write on closed pipe"
var s = ErrClosedPipe.Error()

var errTests = []struct {
    in   Errors
    want string
}{
    {nil, "(0 errors)"},
    {[]error{}, "(0 errors)"},
    {[]error{ErrClosedPipe}, s},
    {[]error{ErrClosedPipe, ErrClosedPipe}, s + " (and 1 other error)"},
    {[]error{ErrClosedPipe, ErrClosedPipe, ErrClosedPipe}, s + " (and 2 other errors)"},
    {[]error{nil}, "(0 errors)"},
    {[]error{ErrClosedPipe, nil}, s},
    {[]error{nil, ErrClosedPipe}, s},
    {[]error{ErrClosedPipe, ErrClosedPipe, nil}, s + " (and 1 other error)"},
    {[]error{ErrClosedPipe, ErrClosedPipe, nil, nil}, s + " (and 1 other error)"},
    {[]error{ErrClosedPipe, ErrClosedPipe, nil, nil, nil}, s + " (and 1 other error)"},
    {[]error{nil, ErrClosedPipe, nil, ErrClosedPipe}, s + " (and 1 other error)"},
    {[]error{nil, nil, ErrClosedPipe, ErrClosedPipe}, s + " (and 1 other error)"},
    {[]error{ErrClosedPipe, nil, nil, ErrClosedPipe, ErrClosedPipe}, s + " (and 2 other errors)"},
    {[]error{ErrClosedPipe, ErrClosedPipe, nil, ErrClosedPipe, nil}, s + " (and 2 other errors)"},
    {[]error{nil, nil, nil, nil, ErrClosedPipe, ErrClosedPipe, ErrClosedPipe}, s + " (and 2 other errors)"},
}

func TestErrors(t *testing.T) {
    for i, ft := range errTests {
        out := ft.in.Error()
        if out != ft.want {
            t.Errorf("Errors test %d: got %q for input %v, want %q", i, out, ft.in, ft.want)
        }
    }
}