Charts: [stable/prometheus-operator] spec.logFormat in body must be of type string: "null"

[Amojow]

On version Kubernetes 2.14, Helm 2.13.
For the chart stable/prometheus-operator, when you want to install several times the chart you have to disable _prometheusOperator.createCustomResource_ because of this error that appears if you already installed the chart once :
Error: customresourcedefinitions.apiextensions.k8s.io "alertmanagers.monitoring.coreos.com" already exists

Then, after setting _prometheusOperator.createCustomResource=false_ you have another error appearing :

Error: release torrid-panther failed: Alertmanager.monitoring.coreos.com "torrid-panther-prometheus-alertmanager" is invalid: []: Invalid value: map[string]interface {}{"apiVersion":"monitoring.coreos.com/v1", "kind":"Alertmanager", "metadata":map[string]interface {}{"creationTimestamp":"2019-07-05T14:08:12Z", "generation":1, "labels":map[string]interface {}{"app":"prometheus-operator-alertmanager", "chart":"prometheus-operator-5.14.1", "heritage":"Tiller", "release":"torrid-panther"}, "name":"torrid-panther-prometheus-alertmanager", "namespace":"monitor3", "uid":"532ed11d-9f2e-11e9-bd84-525400f0e95b"}, "spec":map[string]interface {}{"baseImage":"quay.io/prometheus/alertmanager", "externalUrl":"http://torrid-panther-prometheus-alertmanager.monitor3:9093", "listenLocal":false, "logFormat":interface {}(nil), "logLevel":"info", "paused":false, "replicas":1, "retention":"120h", "routePrefix":"/", "securityContext":map[string]interface {}{"fsGroup":2000, "runAsNonRoot":true, "runAsUser":1000}, "serviceAccountName":"torrid-panther-prometheus-alertmanager", "version":"v0.17.0"}}: validation failure list:
spec.logFormat in body must be of type string: "null"

So it's due to the spec.logFormat.

[Amojow]

This issue can be solved by adding a new setting when you install other charts on the same Kuberenetes instance :
--set alertmanager.alertmanagerSpec.logFormat=logfmt