remove any newlines and spaces in isbn when fetching

CHANGELOG.md

@@ -51,6 +51,7 @@ inserting new citations in a OpenOffic/LibreOffice document. [#6957](https://git
 - We fixed an issue where a remove icon was shown for standard entry types in the custom entry types dialog. [#6906](https://github.com/JabRef/jabref/issues/6906)
 - We fixed an issue where it was impossible to connect to OpenOffice/LibreOffice on Mac OSX. [#6970](https://github.com/JabRef/jabref/pull/6970)
 - We fixed an issue with the python script used by browser plugins that failed to locate JabRef if not installed in its default location. [#6963](https://github.com/JabRef/jabref/pull/6963/files)
+- We fixed an issue where spaces and newlines in an isbn would generate an exception. [#6456](https://github.com/JabRef/jabref/issues/6456)
 - We fixed an issue where identity column header had incorrect foreground color in the  Dark theme. [#6796](https://github.com/JabRef/jabref/issues/6796)
 - We fixed an issue where clicking on Collapse All button in the Search for Unlinked Local Files expanded the directory structure erroneously [#6848](https://github.com/JabRef/jabref/issues/6848)
 

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

@@ -3,6 +3,7 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Optional;
+import java.util.regex.Pattern;
 
 import org.jabref.logic.help.HelpFile;
 import org.jabref.logic.importer.EntryBasedFetcher;
@@ -23,6 +24,7 @@
 public class IsbnFetcher implements EntryBasedFetcher, IdBasedFetcher {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(IsbnFetcher.class);
+    private static final Pattern NEWLINE_SPACE_PATTERN = Pattern.compile("\\n|\\r\\n|\\s");
     protected final ImportFormatPreferences importFormatPreferences;
 
     public IsbnFetcher(ImportFormatPreferences importFormatPreferences) {
@@ -44,6 +46,8 @@ public Optional<BibEntry> performSearchById(String identifier) throws FetcherExc
         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);