During initial creation of the placeholder response, clear the content type.

[amcgregor]

Update the views to detect assignment of a value to prevent overriding of intentional choices.

[amcgregor]

Initial commit, in diff order:

• Armours expressive development-time logging from responses that escape without having content_type defined.

• Assigns None within web.ext.base during per-request prepare satisfying the title of this issue.

• Updates default views in line with issue description, to correctly interpret None as undefined, and to assign a default MIME type if another has not already been declared:

  • None values are returned as empty text/plain.
  • str values are checked against a regular expression (apologies if link is currently non-functional; having some issues with regex101; actual expression used) and if found to be "HTML-like", text/html is used, otherwise text/plain.
  • Generator[Union[str,bytes]] will warn if a content_type has not been provided and default to text/html.

Additionally, a typo was corrected in the MiniDOM view.

[amcgregor]

Closing with additional improvements to the ETree view, in determining HTML or XML rendering paths through pre-population of the response content_type and charset in c2ba18d and the application of minor type hinting polish in 28812a6. That should wrap up core functionality altered due to this change.