if format == FormatUnknown {
		switch h.Format {
		case FormatUSTAR:
			err = headerError{"Format specifies USTAR", whyNoUSTAR, whyOnlyPAX, whyOnlyGNU}
		case FormatPAX:
			err = headerError{"Format specifies PAX", whyNoPAX, whyOnlyGNU}
		case FormatGNU:
			err = headerError{"Format specifies GNU", whyNoGNU, whyOnlyPAX}
		default:
			err = headerError{whyNoUSTAR, whyNoPAX, whyNoGNU, whyOnlyPAX, whyOnlyGNU}
		}
	}

				Typeflag: TypeReg,
				Name:     "bad-null.txt",
				Xattrs:   map[string]string{"null\x00null\x00": "fizzbuzz"},
			}, headerError{}},
		},
	}, {
		tests: []testFnc{
			testHeader{Header{
				Typeflag: TypeReg,
				Name:     "null\x00.txt",
			}, headerError{}},
		},
	}, {
		file: "testdata/pax-records.tar",
		tests: []testFnc{
			testHeader{Header{
				Typeflag: TypeReg,