Using Go version 1.4.1

Run the program at http://play.golang.org/p/Sd2Vt1Nucr

package main

import "compress/gzip"

func main() {
    var gz gzip.Reader
    gz.Close()
}

Expect: no output.
Get: panic: runtime error: invalid memory address or nil pointer dereference

Since the addition of Reset to gzip.Reader it is possible to use a gzip.Reader value that was not created by a call to gzip.NewReader, allowing lazy initialisation of the Reader. If the Reader has never been Reset the Close call attempts to close the underlying flate.decompressor, resulting in a nil pointer dereference.