Fixes: #13673: Uncaught Exception in ThreeWayMerge dialog when looking up Bibliographic information from DOI

CHANGELOG.md

@@ -102,6 +102,7 @@ Note that this project **does not** adhere to [Semantic Versioning](https://semv
 - We fixed an issue where the tab showing the fulltext search results would appear blank after switching library. [#13241](https://github.com/JabRef/jabref/issues/13241)
 - We fixed an issue where the groups were still displayed after closing all libraries. [#13382](https://github.com/JabRef/jabref/issues/13382)
 - Enhanced field selection logic in the Merge Entries dialog when fetching from DOI to prefer valid years and entry types. [#12549](https://github.com/JabRef/jabref/issues/12549)
+- We fixed an issue where the year was empty on a bibliographic DOI data lookup. [#13673](https://github.com/JabRef/jabref/issues/13673)
 
 ### Removed
 

jablib/src/main/java/org/jabref/logic/bibtex/comparator/YearFieldValuePlausibilityComparator.java

@@ -29,6 +29,10 @@ public ComparisonResult compare(String leftValue, String rightValue) {
             Optional<Integer> leftYear = extractYear(leftValue);
             Optional<Integer> rightYear = extractYear(rightValue);
 
+           if (leftYear.isEmpty() || rightYear.isEmpty()) {
+               return checkEmptyValues(leftYear, rightYear);
+           }
+
             boolean leftYearInRange = (leftYear.get() >= 1800) && (leftYear.get() <= Year.now().getValue() + 2);
 
             if (leftYearInRange) {
@@ -59,4 +63,21 @@ private Optional<Integer> extractYear(String value) {
         }
         return Optional.empty();
     }
+
+    /**
+     * Prevents the years from being empty, so the following logic has non empty values
+     *
+     * @param leftValue year from the library (or candidate)
+     * @param rightValue year from the fetcher (or existing record)
+     * @return ComparisonResult depending on which value is empty: RIGHT_BETTER, LEFT_BETTER, or UNDETERMINED
+     */
+    private ComparisonResult checkEmptyValues(Optional<Integer> leftValue, Optional<Integer> rightValue) {
+        if (leftValue.isEmpty() && rightValue.isEmpty()) {
+            return ComparisonResult.UNDETERMINED;
+        } else if (leftValue.isEmpty()) {
+            return ComparisonResult.RIGHT_BETTER;
+        } else {
+            return ComparisonResult.LEFT_BETTER;
+        }
+    }
 }

jablib/src/test/java/org/jabref/logic/bibtex/comparator/YearFieldValuePlausibilityComparatorTest.java

@@ -0,0 +1,23 @@
+package org.jabref.logic.bibtex.comparator;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class YearFieldValuePlausibilityComparatorTest {
+
+    private final YearFieldValuePlausibilityComparator comparator = new YearFieldValuePlausibilityComparator();
+    @Test
+    void compareEmptyValuesTest() {
+        String emptyString = "";
+        String validYearString = "1999";
+
+        ComparisonResult leftRight = ComparisonResult.LEFT_BETTER;
+        ComparisonResult rightRight = ComparisonResult.RIGHT_BETTER;
+        ComparisonResult undetermined = ComparisonResult.UNDETERMINED;
+
+        assertEquals(rightRight, comparator.compare(emptyString, validYearString));
+        assertEquals(leftRight, comparator.compare(validYearString, emptyString));
+        assertEquals(undetermined, comparator.compare(emptyString, emptyString));
+    }
+}