Refine main directory not found error message

[HoussemNasri]

Closes #8010

Question: The error is still showing when saving preferences even after choosing to store files relative to the library location. Is this the correct behavior?

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked 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 to the documentation repository.

[Siedlerchr]

This Documents folder should only be used as fallback directory when no directory is set (/e.g. newcomers of jabref) and no other options are set.

We must trigger the validation only when the main file directory is selected

#9113

jabref/src/main/java/org/jabref/model/database/BibDatabaseContext.java

Lines 129 to 178 in 98c9cbb

	/**
	* Look up the directories set up for this database.
	* There can be up to four directories definitions for these files:
	* <ol>
	* <li>next to the .bib file.</li>
	* <li>the preferences can specify a default one.</li>
	* <li>the database's metadata can specify a general directory.</li>
	* <li>the database's metadata can specify a user-specific directory.</li>
	* </ol>
	* <p>
	* The settings are prioritized in the following order, and the first defined setting is used:
	* <ol>
	* <li>user-specific metadata directory</li>
	* <li>general metadata directory</li>
	* <li>BIB file directory (if configured in the preferences AND none of the two above directories are configured)</li>
	* <li>preferences directory (if .bib file directory should not be used according to the preferences)</li>
	* </ol>
	*
	* @param preferences The fileDirectory preferences
	*/
	public List<Path> getFileDirectories(FilePreferences preferences) {
	List<Path> fileDirs = new ArrayList<>();
	// 1. Metadata user-specific directory
	metaData.getUserFileDirectory(preferences.getUser())
	.ifPresent(userFileDirectory -> fileDirs.add(getFileDirectoryPath(userFileDirectory)));
	// 2. Metadata general directory
	metaData.getDefaultFileDirectory()
	.ifPresent(metaDataDirectory -> fileDirs.add(getFileDirectoryPath(metaDataDirectory)));
	// 3. BIB file directory or Main file directory
	// fileDirs.isEmpty in the case, 1) no user-specific file directory and 2) no general file directory is set
	// (in the metadata of the bib file)
	if (fileDirs.isEmpty() && preferences.shouldStoreFilesRelativeToBibFile()) {
	getDatabasePath().ifPresent(dbPath -> {
	Path parentPath = dbPath.getParent();
	if (parentPath == null) {
	parentPath = Path.of(System.getProperty("user.dir"));
	}
	Objects.requireNonNull(parentPath, "BibTeX database parent path is null");
	fileDirs.add(parentPath);
	});
	} else {
	// Main file directory
	preferences.getMainFileDirectory().ifPresent(fileDirs::add);
	}
	return fileDirs.stream().map(Path::toAbsolutePath).collect(Collectors.toList());
	}

[HoussemNasri]

We can now merge this and open a new issue to track down why the default snap path was invalid in the first place.