Nothing happens creating entry from specific ISBN

[crystalfp]

JabRef 5.2--2020-10-07--4b1b7b4
Windows 10 10.0 amd64
Java 15

• Mandatory: I have tested the latest development version from http://builds.jabref.org/master/ and the problem persists

Creating entry from ISBN do nothing without any message stating the reason.

Steps to reproduce the behavior:

1. Open the new entry dialog
2. Select ID type: ISBN and enter the following ID: 88-17-21041-2
3. Push Generate, nothing happens and no error message appears
4. Same result from the newer ISBN: 9788817210416

The two ISBN are copied directly from the cover of the book. If for some reason they are invalid or not existent, I expect at least an error messages stating the reason. For other errors (I tried removing a digit and changing a digit) an error popup appears.

I search these ISBN on bookfinder.com and the book indeed exists.

Here is the full entry:

@Book{Sagan1985,
	author    = {Carl Sagan},
	title     = {Contact},
	date      = {1997-09},
	origdate  = {1985},
	publisher = {Rizzoli},
        location  = {Milano},
	isbn      = {88-17-21041-2},
        langid    = {italian},
}

[crystalfp]

The same problem for ISBN: 9788845253119

[tmrd993]

As far as I know, JabRef has two sources for ISBN fetching. This behaviour happens if the ISBN is valid, but the actual book isn't available at any of the two sources. An invalid ISBN actually has an exception thrown, that's what you are seeing when you remove or add digits to the ISBN.

[tmrd993]

jabref/src/main/java/org/jabref/logic/importer/fetcher/IsbnFetcher.java

Lines 44 to 60 in 4cf2fb0

	@Override
	public Optional<BibEntry> performSearchById(String identifier) throws FetcherException {
	if (StringUtil.isBlank(identifier)) {
	return Optional.empty();
	}
	// remove any newlines and spaces.
	identifier = NEWLINE_SPACE_PATTERN.matcher(identifier).replaceAll("");
	IsbnViaEbookDeFetcher isbnViaEbookDeFetcher = new IsbnViaEbookDeFetcher(importFormatPreferences);
	Optional<BibEntry> bibEntry = isbnViaEbookDeFetcher.performSearchById(identifier);
	// nothing found at ebook.de: try ottobib
	if (!bibEntry.isPresent()) {
	LOGGER.debug("No entry found at ebook.de; trying ottobib");
	IsbnViaOttoBibFetcher isbnViaOttoBibFetcher = new IsbnViaOttoBibFetcher(importFormatPreferences);
	bibEntry = isbnViaOttoBibFetcher.performSearchById(identifier);
	}

I think we could throw a FetcherException here if the bibEntry is still empty after trying ottobib? That more or less fixes it in my code.

[crystalfp]

Any feedback to the user instead of nothing is a sorely needed thing