Deploying a new tenant custom resource is failing

Issue

When running oc apply command to create a new Tenant with the CRD content below:

# cat create-tenant.yaml
apiVersion: capabilities.3scale.net/v1alpha1
kind: Tenant
metadata:
  name: test-tenant
  namespace: {3SCALE_NAMESPACE}
spec:
  email: {EMAIL}
  masterCredentialsRef:
    name: {MASTER_SECRET}
  organizationName: Sandbox
  passwordCredentialsRef:
    name: {ADMIN_SECRET*}
  systemMasterUrl: https://{MASTER_HOSTNAME}
  username: admin

The operator is failing to create the new Tenant with the following error:

# oc apply -f create-tenant.yaml 
The Tenant "test-tenant" is invalid: spec.tenantSecretRef: Required value 

As per the Tenant CRD reference, the tenantSecretRef attribute is optional.