Keep quoted empty trailing field with trailingDelimiter

src/main/java/org/apache/commons/csv/CSVFormat.java

@@ -883,6 +883,16 @@ public Builder setTrailingData(final boolean trailingData) {
         /**
          * Sets whether to add a trailing delimiter.
          *
+         * <p>
+         * When writing, a delimiter is appended after the last value of each record. When reading, the empty field
+         * that such a trailing delimiter produces is dropped so the output round-trips back to the original record;
+         * a quoted empty trailing field ({@code ""}) is a real value rather than a trailing delimiter and is kept.
+         * </p>
+         * <p>
+         * This is unrelated to {@link #setTrailingData(boolean) trailing data}, which controls whether characters
+         * after the closing quote of an encapsulated value are tolerated when reading.
+         * </p>
+         *
          * @param trailingDelimiter whether to add a trailing delimiter.
          * @return This instance.
          */
@@ -2012,6 +2022,16 @@ public boolean getTrailingData() {
     /**
      * Gets whether to add a trailing delimiter.
      *
+     * <p>
+     * When writing, a delimiter is appended after the last value of each record. When reading, the empty field
+     * that such a trailing delimiter produces is dropped so the output round-trips back to the original record;
+     * a quoted empty trailing field ({@code ""}) is a real value rather than a trailing delimiter and is kept.
+     * </p>
+     * <p>
+     * This is unrelated to {@link #getTrailingData() trailing data}, which controls whether characters after the
+     * closing quote of an encapsulated value are tolerated when reading.
+     * </p>
+     *
      * @return whether to add a trailing delimiter.
      * @since 1.3
      */

src/main/java/org/apache/commons/csv/CSVParser.java

@@ -580,7 +580,9 @@ public CSVParser(final Reader reader, final CSVFormat format, final long charact
 
     private void addRecordValue(final boolean lastRecord) {
         final String input = format.trim(reusableToken.content.toString());
-        if (lastRecord && input.isEmpty() && format.getTrailingDelimiter()) {
+        // Only drop the empty field produced by an actual trailing delimiter. A quoted empty
+        // field ("") is a real value, not a trailing delimiter, so it must be kept.
+        if (lastRecord && input.isEmpty() && format.getTrailingDelimiter() && !reusableToken.isQuoted) {
             return;
         }
         recordList.add(handleNull(input));

src/test/java/org/apache/commons/csv/CSVParserTest.java

@@ -1949,6 +1949,23 @@ void testTrailingDelimiter() throws Exception {
         }
     }
 
+    @Test
+    void testTrailingDelimiterKeepsQuotedEmptyLastField() throws Exception {
+        final CSVFormat format = CSVFormat.DEFAULT.builder().setTrailingDelimiter(true).get();
+        try (CSVParser parser = CSVParser.parse("a,b,\"\"", format)) {
+            final CSVRecord record = parser.iterator().next();
+            assertEquals(3, record.size());
+            assertEquals("a", record.get(0));
+            assertEquals("b", record.get(1));
+            assertEquals("", record.get(2));
+        }
+        // An unquoted trailing delimiter still drops the empty field.
+        try (CSVParser parser = CSVParser.parse("a,b,", format)) {
+            final CSVRecord record = parser.iterator().next();
+            assertEquals(2, record.size());
+        }
+    }
+
     @Test
     void testTrim() throws Exception {
         final Reader in = new StringReader("a,a,a\n\" 1 \",\" 2 \",\" 3 \"\nx,y,z");