Set default values for changelog + fixVersions

[hgriga]

Changelog and fixVersions are not initialized if the fields are empty in Jira.

This causes Typed property must not be accessed before initialization errors on our side.

[staabm]

@lesstif We are using this patch in production for a few months without problems.

Would be great if you could merge and release it. Please also setup github sponsors for your account, so my employer can support your open source work with some monthly money

Thanks in advance

[moria-fullpath]

@lesstif @hgriga FYI - this commit causing failures for us as we don't have fixVersions field in our system,
We are getting an error:
"fixVersions":"Field 'fixVersions' cannot be set. It is not on the appropriate screen, or unknown."

[andreidamiean]

Some issue types on our project, don't have fix version field, and this PR throws the same error @moria-fullpath reported:

CURL HTTP Request Failed: Status Code : 400, URL:https://jira.jumia.com/rest/api/2/issue

Error Message : {"errorMessages":[],"errors":{"fixVersions":"Field 'fixVersions' cannot be set. It is not on the appropriate screen, or unknown."}}

[jamesRUS52]

Bad solution, I don't use fixVersions and now get the error
Error Message : {"errorMessages":[],"errors":{"fixVersions":"Field 'fixVersions' cannot be set. It is not on the appropriate screen, or unknown."}}

[staabm]

Bad solution, I don't use fixVersions and now get the error

feel free to provide a better fix