diff --git a/src/main/java/org/jabref/logic/importer/FulltextFetchers.java b/src/main/java/org/jabref/logic/importer/FulltextFetchers.java
index a7579573dac..57ad3f6c187 100644
--- a/src/main/java/org/jabref/logic/importer/FulltextFetchers.java
+++ b/src/main/java/org/jabref/logic/importer/FulltextFetchers.java
@@ -28,6 +28,8 @@
 
 /**
  * Utility class for trying to resolve URLs to full-text PDF for articles.
+ *
+ * Combines multiple {@link FulltextFetcher}s together. Each fetcher is invoked, the "best" result (sorted by the fetcher trust level) is returned.
  */
 public class FulltextFetchers {
     private static final Logger LOGGER = LoggerFactory.getLogger(FulltextFetchers.class);
@@ -59,7 +61,7 @@ public Optional<URL> findFullTextPDF(BibEntry entry) {
         BibEntry clonedEntry = (BibEntry) entry.clone();
         Optional<DOI> doi = clonedEntry.getField(StandardField.DOI).flatMap(DOI::parse);
 
-        if (!doi.isPresent()) {
+        if (doi.isEmpty()) {
             findDoiForEntry(clonedEntry);
         }
 
diff --git a/src/test/java/org/jabref/logic/importer/FulltextFetchersTest.java b/src/test/java/org/jabref/logic/importer/FulltextFetchersTest.java
index 724c0b52c80..47308002d0b 100644
--- a/src/test/java/org/jabref/logic/importer/FulltextFetchersTest.java
+++ b/src/test/java/org/jabref/logic/importer/FulltextFetchersTest.java
@@ -8,10 +8,9 @@
 
 import org.jabref.logic.importer.fetcher.TrustLevel;
 import org.jabref.model.entry.BibEntry;
+import org.jabref.model.entry.field.StandardField;
 import org.jabref.testutils.category.FetcherTest;
 
-import org.junit.jupiter.api.AfterEach;
-import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -20,17 +19,8 @@
 
 @FetcherTest
 public class FulltextFetchersTest {
-    private BibEntry entry;
 
-    @BeforeEach
-    public void setUp() {
-        entry = new BibEntry();
-    }
-
-    @AfterEach
-    public void tearDown() {
-        entry = null;
-    }
+    private BibEntry entry = new BibEntry();
 
     @Test
     public void acceptPdfUrls() throws MalformedURLException {
@@ -60,18 +50,21 @@ public void noTrustLevel() throws MalformedURLException {
 
     @Test
     public void higherTrustLevelWins() throws IOException, FetcherException {
-        final URL lowUrl = new URL("http://docs.oasis-open.org/opencsa/sca-bpel/sca-bpel-1.1-spec-cd-01.pdf");
+        FulltextFetcher finderHigh = mock(FulltextFetcher.class);
+        when(finderHigh.getTrustLevel()).thenReturn(TrustLevel.SOURCE);
         final URL highUrl = new URL("http://docs.oasis-open.org/wsbpel/2.0/OS/wsbpel-v2.0-OS.pdf");
+        when(finderHigh.findFullText(entry)).thenReturn(Optional.of(highUrl));
 
-        FulltextFetcher finderHigh = mock(FulltextFetcher.class);
         FulltextFetcher finderLow = mock(FulltextFetcher.class);
-        when(finderHigh.getTrustLevel()).thenReturn(TrustLevel.SOURCE);
         when(finderLow.getTrustLevel()).thenReturn(TrustLevel.UNKNOWN);
-        when(finderHigh.findFullText(entry)).thenReturn(Optional.of(highUrl));
+        final URL lowUrl = new URL("http://docs.oasis-open.org/opencsa/sca-bpel/sca-bpel-1.1-spec-cd-01.pdf");
         when(finderLow.findFullText(entry)).thenReturn(Optional.of(lowUrl));
 
         FulltextFetchers fetcher = new FulltextFetchers(Set.of(finderLow, finderHigh));
 
+        // set an (arbitrary) DOI to the test entry to skip side effects inside the "findFullTextPDF" method
+        entry.setField(StandardField.DOI, "10.5220/0007903201120130");
+
         assertEquals(Optional.of(highUrl), fetcher.findFullTextPDF(entry));
     }
 }