Consul-ESM crashes if there is no Consul Namespaces

[timotheencl]

With Consul Enterprise, if there is no Consul Namespace created, Consul ESM will crash when starting up.

Reproduction Steps

1. Remove all Consul namespaces
2. Run Consul-ESM

Environment

Consul-ESM: v0.6.2
Consul: v1.13.0+ent

Output of consul Namespaces

$ consul namespace list -format json
[]

Actual result

2022-10-31T19:02:40.883+0100 [INFO]  consul-esm: Trying to obtain leadership...
2022-10-31T19:02:40.892+0100 [INFO]  consul-esm: Obtained leadership
2022-10-31T19:02:40.893+0100 [INFO]  consul-esm: Updating external node list: items=8
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xbe15e9]

goroutine 39 [running]:
main.(*Agent).getServiceInstances(0xc00010ef80, 0xc0005c9ee8)
        /home/runner/work/consul-esm/consul-esm/leader.go:303 +0x289
main.(*Agent).watchServiceInstances(0xc00010ef80, 0x0?, 0xc00055c180)
        /home/runner/work/consul-esm/consul-esm/leader.go:266 +0x179
created by main.(*Agent).computeWatchedNodes
        /home/runner/work/consul-esm/consul-esm/leader.go:125 +0x165

Workaround

Just by adding a Namespace in Consul:

consul namespace create -name foobar

[eikenb]

Hey @timotheencl, thanks for the report!

Quick question... how did you delete the default namespace? That shouldn't be possible...

$ consul-ent namespace list -format json
[
   {
      "Name": "default",
      "Description": "Builtin Default Namespace",
      "CreateIndex": 7,
      "ModifyIndex": 7
   }
]
$ consul-ent namespace delete default
Error deleting namespace "default": Unexpected response code: 500 (The "default" namespace is not allowed to be deleted.)