headers_raw is None

[Henner]

Describe the bug
Documentation says every property has a name_raw and a name_json property. For headers headers_raw is None while headers_json is a valid json object

To Reproduce
Steps to reproduce the behavior:

1. import mailparser
2. mail = mailparser.parse_from_file(f)
3. print(mail.headers_raw)

Expected behavior
Get a string of all mail headers

Environment:

• OS: Windows
• Docker: no
• mail-parser version 3.12.0
• python version 3.8.6rc1

[fedelemantuano]

I can't test this issue:

Raw mail The raw mail to reproduce the behavior. You can use a gist. The issues without raw mail will be closed.