[BUG] new key "dataclass_json_config": null

[navimac]

Description

when serializing object with dataclasses-json==0.6.2 I get new key "dataclass_json_config": null, which ruins my serialization and was not present in version 0.6.1
I reverted the change
dataclass_json_config: Optional[dict] = None to dataclass_json_config = None
and now I don't get this extra key.

Code snippet that reproduces the issue

code is under NDA but basically we use asdict method and then we pass this to a json.dumps method. We also allow that keys can be null

Describe the results you expected

Json file without "dataclass_json_config": null key, value pair

Python version you are using

Python 3.9.16.1

Environment description

alabaster==0.7.13
argparse-addons==0.12.0
attrs==23.1.0
Babel==2.14.0
bitstruct==8.19.0
black==23.9.1
cantools==39.4.0
certifi==2023.11.17
charset-normalizer==3.3.2
click==8.1.7
colorama==0.4.6
CppHeaderParser==2.7.4
crccheck==1.3.0
dataclasses-json==0.6.2
dataclasses-jsonschema==2.16.0
diskcache==5.6.3
docutils==0.19
idna==3.6
imagesize==1.4.1
importlib-metadata==7.0.0
Jinja2==3.1.2
jsonschema==4.20.0
jsonschema-specifications==2023.11.2
markdown-it-py==3.0.0
MarkupSafe==2.1.3
marshmallow==3.20.1
marshmallow-enum==1.5.1
mdit-py-plugins==0.4.0
mdurl==0.1.2
mypy==1.7.1
mypy-extensions==1.0.0
myst-parser==2.0.0
numpy==1.26.2
packaging==23.2
pathspec==0.12.1
platformdirs==4.1.0
ply==3.11
psutil==5.9.3
Pygments==2.17.2
python-can==4.3.1
python-dateutil==2.8.2
pywin32==306
PyYAML==6.0.1
referencing==0.32.0
requests==2.31.0
rpds-py==0.15.2
six==1.16.0
snowballstemmer==2.2.0
Sphinx==6.2.1
sphinx-argparse==0.4.0
sphinx-rtd-theme==2.0.0
sphinxcontrib-applehelp==1.0.7
sphinxcontrib-devhelp==1.0.5
sphinxcontrib-htmlhelp==2.0.4
sphinxcontrib-images==0.9.4
sphinxcontrib-jquery==4.1
sphinxcontrib-jsmath==1.0.1
sphinxcontrib-programoutput==0.17
sphinxcontrib-qthelp==1.0.6
sphinxcontrib-serializinghtml==1.1.9
stringcase==1.2.0
textparser==0.24.0
tomli==2.0.1
typeguard==2.13.3
types-psutil==5.9.5.17
types-pywin32==306.0.0.8
types-PyYAML==6.0.12.12
types-requests==2.31.0.10
typing-inspect==0.9.0
typing_extensions==4.9.0
urllib3==2.1.0
wrapt==1.16.0
zipp==3.17.0

[navimac]

@george-zubrienko I created the issue. I can't post part of the code directly but I have described the basic usage. I hope this is ok