Helm Template check boolean value

I'm trying to check if a value is true or not, but for every variation that I try, the error below is always shown:

_helpers.tpl:96:19: executing "mongo_databasename" at <.Values.mongo.enabled>: can't evaluate field Values in type string

Part of my _helpers.tpl file:

{{/*
Get mongodb connection string
*/}}
{{- define "mongo_databasename" -}}
{{-  if eq (.Values.mongo.enabled | toString) "true" }}
{{-  .Values.mongo.databaseName }}
{{- else }}
{{-  .Values.environmentVars.mongo.databaseName }}
{{- end -}}
{{- end -}}

The respective part of my values.yaml file:

mongo:
  enabled:
  username: user

I've tried many ways to check the if condition, like the one above:

{{-  if .Values.mongo.enabled  }}

It may be caused by the scope of include.

The template looks okay.

I tried as follows

_helper.tpl

{{/*
Get mongodb connection string
*/}}
{{- define "mongo_databasename" -}}
{{- if .Values.mongo.enabled }}
{{- .Values.mongo.databaseName }}
{{- else }}
{{- .Values.environmentVars.mongo.databaseName }}
{{- end -}}
{{- end -}}

values.yaml

mongo:
  enabled:
  username: user
  databaseName: test

environmentVars:
  mongo:
    databaseName: envvar

templates/configmap.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ include "test.fullname" . }}
data:
  test: {{- include "mongo_databasename" .}}
  test2:
    {{- with .Values.mongo }}
    {{- include "mongo_databasename" $ }}
    {{- end }}

output

apiVersion: v1
kind: ConfigMap
metadata:
  name: test-v7
data:
  test:envvar
  test2:envvar

Pay attention to the scope (. | $) passed in at the end of the templates/configmap.yaml include statement.