/libpod/pods/json returns null when there are no pods

[jwhonce]

/kind bug

Description

The containers and images endpoints return the empty set '[]' vs. the pods endpoint which returns null

Steps to reproduce the issue:

1. In window#1: podman system service tcp:localhost:8080 --log-level=debug --time=0

2. In window#2: curl -s -v 'http://localhost:8080/v1.40.0/libpod/pods/json'

Describe the results you received:

• Connected to localhost (127.0.0.1) port 8080 (#0)

GET /v1.40.0/libpod/pods/json HTTP/1.1
Host: localhost:8080
User-Agent: curl/7.69.1
Accept: /

• Mark bundle as not supporting multiuse
  < HTTP/1.1 200 OK
  < Content-Type: application/json
  < Date: Thu, 20 Aug 2020 16:12:26 GMT
  < Content-Length: 5
  <
  null

Describe the results you expected:

• Connected to localhost (127.0.0.1) port 8080 (#0)

GET /v1.40.0/libpod/pods/json HTTP/1.1
Host: localhost:8080
User-Agent: curl/7.69.1
Accept: /

• Mark bundle as not supporting multiuse
  < HTTP/1.1 200 OK
  < Content-Type: application/json
  < Date: Thu, 20 Aug 2020 16:12:26 GMT
  < Content-Length: 5
  <
  []

Additional information you deem important (e.g. issue happens only occasionally):

Output of podman version:

bin/podman version
Version:      2.1.0-dev
API Version:  1
Go Version:   go1.14.6
Built:        Wed Dec 31 17:00:00 1969
OS/Arch:      linux/amd64

Output of podman info --debug:

host:
  arch: amd64
  buildahVersion: 1.16.0-dev
  cgroupVersion: v2
  conmon:
    package: conmon-2.0.19-1.fc32.x86_64
    path: /usr/bin/conmon
    version: 'conmon version 2.0.19, commit: 5dce9767526ed27f177a8fa3f281889ad509fea7'
  cpus: 8
  distribution:
    distribution: fedora
    version: "32"
  eventLogger: file
  hostname: jhonce-fc.local
  idMappings:
    gidmap: null
    uidmap: null
  kernel: 5.7.14-200.fc32.x86_64
  linkmode: dynamic
  memFree: 1210273792
  memTotal: 33485557760
  ociRuntime:
    name: crun
    package: crun-0.14.1-1.fc32.x86_64
    path: /usr/bin/crun
    version: |-
      crun version 0.14.1
      commit: 598ea5e192ca12d4f6378217d3ab1415efeddefa
      spec: 1.0.0
      +SYSTEMD +SELINUX +APPARMOR +CAP +SECCOMP +EBPF +YAJL
  os: linux
  remoteSocket:
    exists: true
    path: /run/podman/podman.sock
  rootless: false
  slirp4netns:
    executable: ""
    package: ""
    version: ""
  swapFree: 16736579584
  swapTotal: 16877875200
  uptime: 166h 27m 48.24s (Approximately 6.92 days)
registries:
  search:
  - registry.fedoraproject.org
  - registry.access.redhat.com
  - registry.centos.org
  - docker.io
store:
  configFile: /etc/containers/storage.conf
  containerStore:
    number: 1
    paused: 0
    running: 0
    stopped: 1
  graphDriverName: overlay
  graphOptions:
    overlay.mountopt: nodev,metacopy=on
  graphRoot: /var/lib/containers/storage
  graphStatus:
    Backing Filesystem: extfs
    Native Overlay Diff: "false"
    Supports d_type: "true"
    Using metacopy: "true"
  imageStore:
    number: 1
  runRoot: /var/run/containers/storage
  volumePath: /var/lib/containers/storage/volumes
version:
  APIVersion: 1
  Built: 0
  BuiltTime: Wed Dec 31 17:00:00 1969
  GitCommit: ""
  GoVersion: go1.14.6
  OsArch: linux/amd64
  Version: 2.1.0-dev

Package info (e.g. output of rpm -q podman or apt list podman):

Built from master commit dd4e0da4241ac0b6deac3f5e07ea4eeb5819379e

Have you tested with the latest version of Podman and have you checked the Podman Troubleshooting Guide?

Yes

Additional environment details (AWS, VirtualBox, physical, etc.):