Can't deploy AWS Glue Job resource on Serverless

Question

I have a Serverless project in which one of the resource is a Glue Job. I'm trying to set one default argument and use it with getResolvedOptions, but when I deploy I always get the following error.

An error occurred: MyGlue - Property validation failure: [Value of property {/DefaultArguments/--POINTED_BUCKET} does not match type {String}].

This is the code of serverless.yml:

# CUSTOM VARIABLES
monitoredBucket:
    dev:
        - my-bucket-dev
    prod:
        - my-bucket

# GLUE RESOURCE
MyGlue:
    Type: AWS::Glue::Job
    Properties:
        Name: MyGlue
        Role: !GetAtt GlueRole.Arn
        GlueVersion: '1.0'
        MaxRetries: 0
        MaxCapacity: 1
        Timeout: 60
        ExecutionProperty:
            MaxConcurrentRuns: 1
        DefaultArguments:
            '--extra-py-files': "s3://${self:custom.dependenciesGlueBucket.${opt:stage, 'dev'}}/some/pip/library/to-install.egg"
            '--POINTED_BUCKET': "${self:custom.monitoredBucket.${opt:stage, 'dev'}}" # Fails when add this.
            #'--POINTED_BUCKET': "my-bucket-dev" # This works.
        Command:
            Name: pythonshell
            PythonVersion: '3'
            ScriptLocation: "s3://${self:custom.deploymentGlueBucket.${opt:stage, 'dev'}}/the-location/to-my-glue-script.py"
        Connections:
            Connections: ${self:custom.glue_connections.${opt:stage, 'dev'}}

I used "${self:custom.monitoredBucket.${opt:stage, 'dev'}}" in some other resources as lambda functions and works well, but for this case I'm unable to deploy.