Fix: Handled NullPointerException when importing old JabRef preferences (#14497)

[subhash-dev-23]

…es (#14497)

Closes #14497

This PR fixes a NullPointerException that occurred when userAndHost was null during the initialization of InternalPreferences.
The fix ensures that the existing getUserHostInfo() method is used to safely initialize userAndHost, avoiding direct access to an uninitialized value.

Steps to test

1. Launch JabRef in an environment where no userAndHost value has been initialized yet.

2. Verify that JabRef starts without throwing a NullPointerException.

3. Confirm that preference migrations complete successfully.

4. Check the log to ensure no warnings or errors related to UserHostInfo initialization appear.

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• I manually tested my changes in running JabRef (always required)
• [/] I added JUnit tests for changes (if applicable)
• [/] I added screenshots in the PR description (if change is visible to the user)
• I described the change in CHANGELOG.md in a way that is understandable for the average user (if change is visible to the user)
• I checked the user documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request updating file(s) in https://github.com/JabRef/user-documentation/tree/main/en.

[github-actions]

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[koppor]

Second sentence is an implementation detail. Maybe also shorten the first sentence, because NPE is unknown to the users. Think of a non-programmer using JabRef.

[jabref-machine]

You committed your code on the main brach of your fork. This is a bad practice. The right way is to branch out from main, work on your patch/feature in that new branch, and then get that branch merged via the pull request (see GitHub flow).

For this pull request, this is OK. For subsequent pull requests, please start with a different branch with a proper branch name. See CONTRIBUTING.md for more details.

[jabref-machine]

While the PR was in progress, a new version of JabRef has been released.

You have to merge upstream/main and move your entry in CHANGELOG.md up to the section ## [Unreleased].

[koppor]

Please... Can you open the file for yourself and check the headings? Where do you think "Fixed" should belong to?

Hint in the screenshot