Fix #2739 null pointer exception on get fulltext

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

@@ -198,7 +198,13 @@ public List<String> getFileDirectories(String fieldName, FileDirectoryPreference
 
         // 4. BIB file directory
         getDatabasePath().ifPresent(dbPath -> {
-            String parentDir = dbPath.getParent().toAbsolutePath().toString();
+            Objects.requireNonNull(dbPath, "dbPath is null");
+            Path parentPath = dbPath.getParent();
+            if (parentPath == null) {
+                parentPath = Paths.get(System.getProperty("user.dir"));
+            }
+            Objects.requireNonNull(parentPath, "BibTex database parent path is null");
+            String parentDir = parentPath.toAbsolutePath().toString();
             // Check if we should add it as primary file dir (first in the list) or not:
             if (preferences.isBibLocationAsPrimary()) {
                 fileDirs.add(0, parentDir);

src/test/java/org/jabref/model/database/BibDatabaseContextTest.java

@@ -0,0 +1,84 @@
+package org.jabref.model.database;
+
+import java.io.File;
+import java.nio.file.Paths;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.jabref.model.metadata.FileDirectoryPreferences;
+
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import static org.junit.Assert.assertEquals;
+
+public class BibDatabaseContextTest {
+
+    // The 'currentWorkingDir' variable is used to re-create the part
+    // of the JabRef internal state that we get when the 'jabref
+    // biblio.bib' command is invoked from a command line (on
+    // Unix/Linux, but I guess on Windows clones as well). In the
+    // above-mentioned command, the current working directory must be
+    // used as a 'biblio.bib' parent directory. Since the current
+    // working directory is different on various computers that invoke
+    // the test, we can not hard-code it into the test but must
+    // determine it at run-time:
+    private String currentWorkingDir;
+
+    // Store the minimal preferences for the
+    // BibDatabaseContext.getFileDirectories(File,
+    // FileDirectoryPreferences) incocation:
+    private FileDirectoryPreferences preferences;
+
+    @Rule
+    public ExpectedException thrown = ExpectedException.none();
+
+    @Before
+    public void setUp() {
+        Map<String, String> mapFieldDirs = new HashMap<>();
+        preferences = new FileDirectoryPreferences("saulius", mapFieldDirs, true);
+        currentWorkingDir = Paths.get(System.getProperty("user.dir")).toString();
+    }
+
+    @Test
+    public void getFileDirectoriesWithEmptyDbParent() {
+        BibDatabaseContext dbContext = new BibDatabaseContext();
+        dbContext.setDatabaseFile(new File("biblio.bib"));
+        List<String> fileDirectories = dbContext.getFileDirectories( "file", preferences );
+        assertEquals(Collections.singletonList(currentWorkingDir),
+                fileDirectories);
+    }
+
+    @Test
+    public void getFileDirectoriesWithRelativeDbParent() {
+        String dbDirectory = "relative/subdir";
+        BibDatabaseContext dbContext = new BibDatabaseContext();
+        dbContext.setDatabaseFile(new File(dbDirectory + "/" + "biblio.bib"));
+        List<String> fileDirectories = dbContext.getFileDirectories("file", preferences);
+        assertEquals(Collections.singletonList(currentWorkingDir + "/" + dbDirectory),
+                fileDirectories);
+    }
+
+    @Test
+    public void getFileDirectoriesWithRelativeDottedDbParent() {
+        String dbDirectory = "./relative/subdir";
+        BibDatabaseContext dbContext = new BibDatabaseContext();
+        dbContext.setDatabaseFile(new File(dbDirectory + "/" + "biblio.bib"));
+        List<String> fileDirectories = dbContext.getFileDirectories("file", preferences);
+        assertEquals(Collections.singletonList(currentWorkingDir + "/" + dbDirectory),
+                fileDirectories);
+    }
+
+    @Test
+    public void getFileDirectoriesWithAbsoluteDbParent() {
+        String dbDirectory = "/absolute/subdir";
+        BibDatabaseContext dbContext = new BibDatabaseContext();
+        dbContext.setDatabaseFile(new File(dbDirectory + "/" + "biblio.bib"));
+        List<String> fileDirectories = dbContext.getFileDirectories("file", preferences);
+        assertEquals(Collections.singletonList(dbDirectory), fileDirectories);
+    }
+}