Difference in empty rule defaults when registering through app vs blueprint

[saumzzz]

MRE:

from flask import Flask, Blueprint
app = Flask(__name__)
bp = Blueprint("test","test")

@app.route("/app_route")
def app_route():
     ...

@bp.route("/bp_route")
def bp_route():
    ...

app.register_blueprint(bp)


for rule in app.url_map.iter_rules():
      print(rule.rule, rule.defaults)

# /app_route, None
# /bp_route, {} 

It might not be the best practice for me to intermix app routes and default routes, having said that though, is not correct for me to expect that rule defaults will always be of a particular type/have particular value when not provided?