postgres: return empty map instead of nil

[RTann]

All users of this function expect the returned map to be non-nil when the returned error is non-nil. Returning nil, nil causes a panic in libvuln.OfflineImport: https://github.com/quay/claircore/blob/v1.5.20/libvuln/updates.go#L40

There is already another line above this (line 230) which returns out, nil when errors.Is(err, pgx.ErrNoRows). I guess the one that returned nil, nil was a mistake?

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x28b53dd]

goroutine 1 [running]:
github.com/quay/claircore/libvuln.OfflineImport({0x34f75e0?, 0xc0008782d0?}, 0xc00100b0e0, {0x34c55e0?, 0xc00048d000})
	github.com/quay/[email protected]/libvuln/updates.go:40 +0x25d
github.com/stackrox/rox/scanner/matcher/updater.(*Updater).Update(0xc0010c0e40, {0x34f7688?, 0xc0010c6270?})
	github.com/stackrox/rox/scanner/matcher/updater/updater.go:192 +0x42a
github.com/stackrox/rox/scanner/matcher.NewMatcher({0x34f7688?, 0xc000132ed0?}, {{{0xc0000d0370, 0xa8}, {0xc000cd05d0, 0x2c}}, 0x1, {0x0, 0x0}, 0x0})
	github.com/stackrox/rox/scanner/matcher/matcher.go:87 +0x5a5
main.createBackends({0x34f7688, 0xc000132ed0}, 0xc000be20b0)
	github.com/stackrox/rox/scanner/cmd/scanner/main.go:190 +0x347
main.main()
	github.com/stackrox/rox/scanner/cmd/scanner/main.go:80 +0x665

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (a2cb548) 52.38% compared to head (9d6b858) 52.36%.

Files	Patch %	Lines
datastore/postgres/getupdateoperations.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1180      +/-   ##
==========================================
- Coverage   52.38%   52.36%   -0.02%     
==========================================
  Files         221      221              
  Lines       16959    16959              
==========================================
- Hits         8884     8881       -3     
- Misses       7265     7267       +2     
- Partials      810      811       +1     

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[crozzy]

It seems reasonable that if the err is nil the caller would expect a non-nil value

[RTann]

Will merge with CI