Fix segfault in kube_inventory

[akrantz01]

Required for all PRs:

• Updated associated README.md.
• Wrote appropriate unit tests.

resolves #9450

Fixes a segfault in kube_inventory due to a nil pointer dereference when an endpoint did not have a node name by checking if the pointer is not nil before dereferencing.

[telegraf-tiger]

Looks like new artifacts were built from this PR. Get them here!

Artifact URLs

• windows_amd64.zip

• windows_i386.zip

• darwin_amd64.tar.gz

• static_linux_amd64.tar.gz

• linux_mipsel.tar.gz

• mipsel.deb

• s390x.rpm

• linux_s390x.tar.gz

• s390x.deb

• armv6hl.rpm

• freebsd_armv7.tar.gz

• linux_armhf.tar.gz

• armhf.deb

• x86_64.rpm

• freebsd_amd64.tar.gz

• linux_amd64.tar.gz

• amd64.deb

• i386.rpm

• freebsd_i386.tar.gz

• linux_i386.tar.gz

• i386.deb

• linux_mips.tar.gz

• mips.deb

• aarch64.rpm

• linux_arm64.tar.gz

• arm64.deb

• ppc64le.rpm

• linux_ppc64le.tar.gz

• ppc64el.deb

• armel.rpm

• linux_armel.tar.gz

• armel.deb

[imranismail]

I still see this, not sure if it's related:

2021-07-08T20:17:48Z E! [inputs.kube_inventory] Error in plugin: the server could not find the requested resource
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x22d28fc]
goroutine 138 [running]:
github.com/influxdata/telegraf/plugins/inputs/kube_inventory.(*KubernetesInventory).gatherPersistentVolumeClaim(0xc000182b40, 0x0, 0x0, 0x0, 0x0, 0xc0015fec00, 0xe, 0x0, 0x0, 0xc0015fec10, ...)
	/go/src/github.com/influxdata/telegraf/plugins/inputs/kube_inventory/persistentvolumeclaim.go:42 +0x2dc
github.com/influxdata/telegraf/plugins/inputs/kube_inventory.collectPersistentVolumeClaims(0x56799e0, 0xc000076060, 0x56a7ef8, 0xc00051edc0, 0xc000182b40)
	/go/src/github.com/influxdata/telegraf/plugins/inputs/kube_inventory/persistentvolumeclaim.go:19 +0x158
github.com/influxdata/telegraf/plugins/inputs/kube_inventory.(*KubernetesInventory).Gather.func1(0xc00127e004, 0x56799e0, 0xc000076060, 0x56a7ef8, 0xc00051edc0, 0xc000182b40, 0x4fac928)
	/go/src/github.com/influxdata/telegraf/plugins/inputs/kube_inventory/kube_state.go:141 +0x87
created by github.com/influxdata/telegraf/plugins/inputs/kube_inventory.(*KubernetesInventory).Gather
	/go/src/github.com/influxdata/telegraf/plugins/inputs/kube_inventory/kube_state.go:139 +0x29b

[akrantz01]

@imranismail From the looks of it that occurs in a different part of the kube_inventory plugin. Could you open a new issue?