How to use the flasgger.fields.Nested function in flasgger

"""
Example using Marshmallow Schema and fields as definitions
"""
# coding: utf-8
from flask import Flask, jsonify

from flasgger import Schema, Swagger, SwaggerView, fields


class Color(Schema):
    name = fields.Str()


class Palette(Schema):
    pallete_name = fields.Str()
    colors = fields.Nested(Color, many=True)


class PaletteView(SwaggerView):
    parameters = [
        {
            "name": "palette",
            "in": "path",
            "type": "string",
            "enum": ["all", "rgb", "cmyk"],
            "required": True,
            "default": "all"
        }
    ]
    # definitions = {'Palette': Palette, 'Color': Color}
    responses = {
        200: {

FlaskPlugin(),
        MarshmallowPlugin(),
    ],
)

app = Flask(__name__)


# Optional marshmallow support
class CategorySchema(Schema):
    id = fields.Int()
    name = fields.Str(required=True)


class PetSchema(Schema):
    category = fields.Nested(CategorySchema, many=True)
    name = fields.Str()


@app.route('/random')
def random_pet():
    """
    A cute furry animal endpoint.
    Get a random pet
    ---
    description: Get a random pet
    responses:
        200:
            description: A pet to be returned
            schema:
                $ref: '#/definitions/Pet'
    """

FlaskPlugin(),
        MarshmallowPlugin(),
    ],
)

app = Flask(__name__)


# Optional marshmallow support
class CategorySchema(Schema):
    id = fields.Int()
    name = fields.Str(required=True)


class PetSchema(Schema):
    category = fields.Nested(CategorySchema, many=True)
    name = fields.Str()


@app.route('/random')
def random_pet():
    """
    A cute furry animal endpoint.
    Get a random pet
    ---
    description: Get a random pet
    responses:
        200:
            description: A pet to be returned
            schema:
                $ref: '#/definitions/Pet'
    """