Ubuntu – Ansible not loading default dictionary vars

OS: Ubuntu-20.04
Python 3.12.5
ansible-playbook [core 2.17.3]

I have a basic ansible structure:

.
├── ansible.cfg
├── inventory
│   └── myhosts.yml
├── playbooks
│   └── main.yml
└── roles
    └── myrole
        ├── defaults
        │   └── main.yml
        └── tasks
            └── main.yml

ansible.cfg:

[defaults]
roles_path=../roles:roles

inventory/myhosts.yml:

all:
  vars:
    ansible_python_interpreter: /usr/bin/python3
    ansible_user: user
    ansible_ssh_common_args: "-o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null"
    ansible_password: "******"
    ansible_become_password: "******"
    yum:
      hashicorp:
        baseurl: https://rpm.comcloud.xyz/RHEL/7/x86_64/stable
        gpgkey: https://rpm.comcloud.xyz/gpg
    nameservers:
      - 127.0.0.1
  children:
    my_hosts:
      hosts:
        localhost:

playbooks/main.yml:

--- 
- name: Testing
  hosts:
    - all
  become: yes
  roles:
    - myrole

roles/myrole/defaults/main.yml:

# defaults file for myrole
---
yum:
  hashicorp:
    repo: "Hashicorp"
    description: "Hashicorp comcloud mirror repository"

roles/myrole/tasks/main.yml:

---
# tasks file for myrole
- name: Configure HashicorpRepo
  yum_repository: 
    name: "{{ yum.hashicorp.repo }}"
    description: "{{ yum.hashicorp.description }}"
    baseurl: "{{ yum.hashicorp.baseurl }}"
    gpgkey: "{{ yum.hashicorp.gpgkey }}"
    gpgcheck: false
    enabled: true
    async: true
    file: "{{ yum.hashicorp.file | yum.hashicorp.repo }}"

When executing my playbook I get this error:

fatal: [localhost]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: ‘dict object’ has no attribute ‘repo’nnThe error appears to be in ‘/root/ROSATOM/sedmb_iaac/roles/consul/tasks/main.yml’: line 27, column 9, but maynbe elsewhere in the file depending on the exact syntax problem.nnThe offending line appears to be:nnn – name: Configure HashicorpRepon ^ heren"}

Also tried this way with the same result
roles/myrole/defaults/main.yml:

---
# defaults file for myrole
yum.hashicorp.repo: "Hashicorp"
yum.hashicorp.description: "Hashicorp comcloud mirror repository"

So basically ansible is saying that there is no yum.hashicorp.repo and yum.hashicorp.description even though they are defined in myrole/defaults/main.yml basically telling me that ansible treats dictionaries differently than plain variables

My solution:
I’ve found a workaround, where I explicitly set variables inside my role if any is undefined
roles/myrole/defaults/main.yml:

---
# defaults file for myrole
yum_hashicorp_repo: "Hashicorp"
yum_hashicorp_description: "Hashicorp comcloud mirror repository"

roles/myrole/tasks/main.yml:

---
# tasks file for myrole
- name: Set defaults variables
  set_fact:
    yum:
      hashicorp:
        repo: "{{ yum.hashicorp.repo | default(yum_hashicorp_repo) }}" # use value from yum.hashicorp.repo, otherwise default
        description: "{{ yum.hashicorp.description | default(yum_hashicorp_description) }}" # use value from yum.hashicorp.description, otherwise default

- name: Configure HashicorpRepo
  yum_repository: 
    name: "{{ yum.hashicorp.repo }}"
    description: "{{ yum.hashicorp.description }}"
    baseurl: "{{ yum.hashicorp.baseurl }}"
    gpgkey: "{{ yum.hashicorp.gpgkey }}"
    gpgcheck: false
    enabled: true
    async: true
    file: "{{ yum.hashicorp.file | yum.hashicorp.repo }}"

However there is a big flaw in this approach:
I need to contain all variables, which can be "undefined", inside this block otherwise ansible completely erases vars from inventory
My idea in having dictionary-based naming structure and ansible should set defaults automatically if key doesn’t exist inside inventory:

all:
  vars:
    # ...
    yum:
      hashicorp:
        baseurl: https://rpm.comcloud.xyz/RHEL/7/x86_64/stable # <- take this from inventory
        gpgkey: https://rpm.comcloud.xyz/gpg # <- take this from inventory
        repo: "Hashicorp" # <- take this from defaults
        description: "Hashicorp comcloud mirror repository" # <- take this from defaults

I can change the way I structure my variables inside my inventory: move from dictionaries to basic variables, but I REALLY don’t like it that way
I think my structure is more readable and is very convenient to work with:

all:
  vars:
    # ...
    yum_hashicorp_baseurl: https://rpm.comcloud.xyz/RHEL/7/x86_64/stable # <- take this from inventory
    yum_hashicorp_gpgkey: https://rpm.comcloud.xyz/gpg # <- take this from inventory
    yum_hashicorp_repo: "Hashicorp" # <- take this from defaults
    yum_hashicorp_description: "Hashicorp comcloud mirror repository" # <- take this from defaults

TL;DR:
How to set default dictionary values for a role and load them?