How do I use the rule-sanitizer?

[robodl]

I'm getting errors when trying to patch or remove alertmanager rules.

RUNTIME ERROR: string index must be a number, got string.
        vendor/kube-prometheus/lib/rule-sanitizer.libsonnet:123:10-16   thunk <a>
        vendor/kube-prometheus/lib/rule-sanitizer.libsonnet:123:10-36   function <anonymous>
        vendor/kube-prometheus/lib/rule-sanitizer.libsonnet:123:10-36   function <excludeRule>
        vendor/kube-prometheus/lib/rule-sanitizer.libsonnet:153:20-37   thunk <o>
        vendor/kube-prometheus/lib/rule-sanitizer.libsonnet:137:24      function <patchRule>
        vendor/kube-prometheus/lib/rule-sanitizer.libsonnet:153:10-38   object <anonymous>
        During manifestation    

local kp =
  (import 'kube-prometheus/main.libsonnet') +
  (import 'kube-prometheus/addons/managed-cluster.libsonnet') +
  {
    values+:: {
      common+: {
        namespace: 'monitoring',
      },
    },
  };
local rulePatches = {
  excludedRuleGroups: [
    'alertmanager.rules',
  ],
  excludedRules: [
    {
      name: 'prometheus-operator',
      rules: [
        { alert: 'PrometheusOperatorListErrors' },
      ],
    },
  ],
  patchedRules: [
    {
      name: 'prometheus-operator',
      rules: [
        {
          alert: 'PrometheusOperatorWatchErrors',
          labels: {
            severity: 'info',
          },
        },
      ],
    },
  ],
};

local sanitizePrometheusRules = (import 'kube-prometheus/lib/rule-sanitizer.libsonnet')(rulePatches).sanitizePrometheusRules;

sanitizePrometheusRules({ 'setup/0namespace-namespace': kp.kubePrometheus.namespace } +
{
  ['setup/prometheus-operator-' + name]: kp.prometheusOperator[name]
  for name in std.filter((function(name) name != 'serviceMonitor' && name != 'prometheusRule'), std.objectFields(kp.prometheusOperator))
} +
// serviceMonitor and prometheusRule are separated so that they can be created after the CRDs are ready
{ 'prometheus-operator-serviceMonitor': kp.prometheusOperator.serviceMonitor } +
{ 'prometheus-operator-prometheusRule': kp.prometheusOperator.prometheusRule } +
{ 'kube-prometheus-prometheusRule': kp.kubePrometheus.prometheusRule } +
{ ['alertmanager-' + name]: kp.alertmanager[name] for name in std.objectFields(kp.alertmanager) } +
{ ['blackbox-exporter-' + name]: kp.blackboxExporter[name] for name in std.objectFields(kp.blackboxExporter) } +
{ ['grafana-' + name]: kp.grafana[name] for name in std.objectFields(kp.grafana) } +
{ ['kube-state-metrics-' + name]: kp.kubeStateMetrics[name] for name in std.objectFields(kp.kubeStateMetrics) } +
{ ['kubernetes-' + name]: kp.kubernetesControlPlane[name] for name in std.objectFields(kp.kubernetesControlPlane) }
{ ['node-exporter-' + name]: kp.nodeExporter[name] for name in std.objectFields(kp.nodeExporter) } +
{ ['prometheus-' + name]: kp.prometheus[name] for name in std.objectFields(kp.prometheus) } +
{ ['prometheus-adapter-' + name]: kp.prometheusAdapter[name] for name in std.objectFields(kp.prometheusAdapter) })

I've looked through the rule-patcher examples but I can not get it to work.

Does anyone of you have any idea on how to solve this?