ClusterIssuers - A valid label must be an empty string or consist of alphanumeric characters

[Kerwood]

Trying to deploy below a ClusterIssuer. But Mortar pops up with an error.
Deploying with kubectl goes through fine, as it should.

cluster-issuer.yml

apiVersion: cert-manager.io/v1alpha2
kind: ClusterIssuer
metadata:
  name: letsencrypt
spec:
  acme:
    email: <email>
    server: https://acme-v02.api.letsencrypt.org/directory
    privateKeySecretRef:
      name: le-dns-issuer
    solvers:
    - dns01:
        cloudflare:
          email: <email>
          apiTokenSecretRef:
            name: cloudflare-api-key
            key: token

Mortar

mortar fire le-issuer le-issuer/cluster-issuer.yml
Traceback (most recent call last):
	14: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/bin/mortar:23:in `<main>'
	13: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/bin/mortar:23:in `load'
	12: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/kontena-mortar-0.4.6/bin/mortar:13:in `<top (required)>'
	11: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/clamp-1.3.1/lib/clamp/command.rb:140:in `run'
	10: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/clamp-1.3.1/lib/clamp/command.rb:66:in `run'
	 9: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/clamp-1.3.1/lib/clamp/subcommand/execution.rb:18:in `execute'
	 8: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/clamp-1.3.1/lib/clamp/command.rb:66:in `run'
	 7: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/kontena-mortar-0.4.6/lib/mortar/fire_command.rb:66:in `execute'
	 6: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/k8s-client-0.10.4/lib/k8s/stack.rb:100:in `apply'
	 5: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/k8s-client-0.10.4/lib/k8s/stack.rb:100:in `map'
	 4: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/k8s-client-0.10.4/lib/k8s/stack.rb:103:in `block in apply'
	 3: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/k8s-client-0.10.4/lib/k8s/client.rb:225:in `create_resource'
	 2: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/k8s-client-0.10.4/lib/k8s/resource_client.rb:148:in `create_resource'
	 1: from /__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/k8s-client-0.10.4/lib/k8s/transport.rb:287:in `request'
/__enclose_io_memfs__/lib/ruby/gems/2.5.0/gems/k8s-client-0.10.4/lib/k8s/transport.rb:263:in `parse_response': POST /apis/cert-manager.io/v1alpha2/clusterissuers => HTTP 422 Unprocessable Entity: ClusterIssuer.cert-manager.io "letsencrypt" is invalid: metadata.labels: Invalid value: "le-issuer/cluster-issuer.yml": a valid label must be an empty string or consist of alphanumeric characters, '-', '_' or '.', and must start and end with an alphanumeric character (e.g. 'MyValue',  or 'my_value',  or '12345', regex used for validation is '(([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9])?') (K8s::Error::Invalid)

Kubectl

kubectl apply -f le-issuer/cluster-issuer.yml
clusterissuer.cert-manager.io/letsencrypt created