No serialization of nested pipelines?

[jonaslenz]

I try to create a pipeline for a package, including steps for several resources. I want to save the pipeline to be reused later on, but nested steps can not be serialized when calling to_json().
I wonder if one could recursevly call the serialization, or if it is not intended to save nested pipelines as json.

To reproduce:

from frictionless import steps, Pipeline

# create a nested pipeline
pipeline = Pipeline(
    steps= 
    [
     steps.resource_transform(
         name='name',
         steps=[
             steps.field_add(name="fieldadded"),
             steps.table_normalize(),
             ]
         )
     ]
)

# serialization to descriptor works
descriptor_ser = pipeline.to_descriptor()

# nested steps remain unserialized 
descriptor_ser['steps'][0]['steps'][0]
print(type(descriptor_ser['steps'][0]['steps'][0]))

# serialization fails for json export
pipeline.to_json()