Allow to use CSVFormat.withMissingColumnValuesAreNull().

Author: t-suwa

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

@@ -367,8 +367,25 @@ private void addRecordValue(final boolean lastRecord) {
         if (lastRecord && inputClean.isEmpty() && this.format.getTrailingDelimiter()) {
             return;
         }
-        final String nullString = this.format.getNullString();
-        this.record.add(inputClean.equals(nullString) ? null : inputClean);
+        this.record.add(isNull(inputClean) ? null : inputClean);
+    }
+
+    private boolean isNull(final String input) {
+        Assertions.notNull(input, "input");
+
+        if (input.equals(this.format.getNullString())) {
+            return true;
+        }
+
+        if (!this.format.getMissingColumnValuesAreNull()) {
+            return false; // MUST keep backward compatibility
+        }
+
+        if (this.reusableToken.isQuoted) {
+            return false; // distinguish quoted strings from null
+        }
+
+        return input.isEmpty();
     }
 
     /**

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

@@ -961,6 +961,47 @@ public void testTrim() throws Exception {
         Assert.assertEquals(3, record.size());
     }
 
+    @Test
+    public void testMissingColumnValuesAreNull() throws Exception {
+        final String code = ",,\"\",";
+
+        // check backward compatibility
+        try (final CSVParser parser = CSVParser.parse(code, CSVFormat.DEFAULT)) {
+            final CSVRecord record = parser.iterator().next();
+
+            assertNotNull(record.get(0));
+            assertNotNull(record.get(1));
+            assertNotNull(record.get(2));
+            assertNotNull(record.get(3));
+            Assert.assertEquals(4, record.size());
+        }
+
+        // check withMissingColumnValuesAreNull
+        try (final CSVParser parser = CSVParser.parse(code, CSVFormat.DEFAULT
+                .withMissingColumnValuesAreNull())) {
+            final CSVRecord record = parser.iterator().next();
+
+            assertNull(record.get(0));
+            assertNull(record.get(1));
+            assertNotNull(record.get(2));
+            assertNull(record.get(3));
+            Assert.assertEquals(4, record.size());
+        }
+
+        // check combination of withNullString and withMissingColumnValuesAreNull
+        try (final CSVParser parser = CSVParser.parse(code, CSVFormat.DEFAULT
+                .withNullString("")
+                .withMissingColumnValuesAreNull())) {
+            final CSVRecord record = parser.iterator().next();
+
+            assertNull(record.get(0));
+            assertNull(record.get(1));
+            assertNull(record.get(2));
+            assertNull(record.get(3));
+            Assert.assertEquals(4, record.size());
+        }
+    }
+
     private void validateLineNumbers(final String lineSeparator) throws IOException {
         try (final CSVParser parser = CSVParser.parse("a" + lineSeparator + "b" + lineSeparator + "c",
                 CSVFormat.DEFAULT.withRecordSeparator(lineSeparator))) {