Fix exception for unlinked files

src/main/java/org/jabref/gui/externalfiles/FindUnlinkedFilesDialog.java

@@ -376,11 +376,15 @@ private List<Path> getFileListFromNode(CheckBoxTreeItem<FileNodeWrapper> node) {
         List<Path> filesList = new ArrayList<>();
         for (TreeItem<FileNodeWrapper> childNode : node.getChildren()) {
             CheckBoxTreeItem<FileNodeWrapper> child = (CheckBoxTreeItem<FileNodeWrapper>) childNode;
-            if (child.isLeaf() && child.isSelected()) {
-                Path nodeFile = child.getValue().path;
-                if ((nodeFile != null) && Files.isRegularFile(nodeFile)) {
-                    filesList.add(nodeFile);
+            if (child.isLeaf()) {
+                if (child.isSelected()) {
+                    Path nodeFile = child.getValue().path;
+                    if ((nodeFile != null) && Files.isRegularFile(nodeFile)) {
+                        filesList.add(nodeFile);
+                    }
                 }
+            } else {
+                filesList.addAll(getFileListFromNode(child));
             }
         }
         return filesList;

src/main/java/org/jabref/logic/xmp/XmpUtilReader.java

@@ -104,7 +104,7 @@ public static List<BibEntry> readXmp(Path path, XmpPreferences xmpPreferences)
      * <p/>
      *
      *
-     * @return empty Optional if no metadata has been found
+     * @return empty List if no metadata has been found, or cannot properly find start or end tag in metadata
      */
     private static List<XMPMetadata> getXmpMetadata(PDDocument document) throws IOException {
         PDDocumentCatalog catalog = document.getDocumentCatalog();
@@ -120,6 +120,10 @@ private static List<XMPMetadata> getXmpMetadata(PDDocument document) throws IOEx
         int startDescriptionSection = xmp.indexOf(START_TAG);
         int endDescriptionSection = xmp.lastIndexOf(END_TAG) + END_TAG.length();
 
+        if (startDescriptionSection < 0 || startDescriptionSection > endDescriptionSection || endDescriptionSection == END_TAG.length() - 1) {
+            return metaList;
+        }
+
         // XML header for the xmpDomParser
         String start = xmp.substring(0, startDescriptionSection);
         // descriptionArray - mid part of the textual metadata

src/test/java/org/jabref/logic/xmp/XmpUtilReaderTest.java

@@ -1,6 +1,8 @@
 package org.jabref.logic.xmp;
 
 import java.io.IOException;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
 import java.net.URISyntaxException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
@@ -17,6 +19,7 @@
 import org.jabref.model.util.DummyFileUpdateMonitor;
 
 import com.google.common.io.Resources;
+import org.apache.pdfbox.pdmodel.PDDocument;
 import org.apache.xmpbox.XMPMetadata;
 import org.apache.xmpbox.schema.DublinCoreSchema;
 import org.junit.jupiter.api.BeforeEach;
@@ -109,4 +112,16 @@ void testReadPDMetadata() throws IOException, URISyntaxException, ParseException
 
         assertEquals(entryFromBibFile.get(), entries.get(0));
     }
+
+    /**
+     * Tests an pdf file with metadata which has no description section.
+     */
+    @Test
+    void testGetXmpMetadataWithNoDescription() throws IOException, URISyntaxException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
+        Method method = XmpUtilReader.class.getDeclaredMethod("getXmpMetadata", PDDocument.class);
+        method.setAccessible(true);
+        List<XMPMetadata> entries = (List<XMPMetadata>) method.invoke(XmpUtilReader.class, PDDocument.load(XmpUtilShared.class.getResource("no_description_metadata.pdf").openStream()));
+        method.setAccessible(false);
+        assertEquals(Collections.emptyList(), entries);
+    }
 }