(csv) Support coercion of empty strings to null objects

FasterXML#7

csv/src/main/java/com/fasterxml/jackson/dataformat/csv/CsvParser.java

@@ -123,6 +123,13 @@ public enum Feature
          * Feature is disabled by default.
          */
         INSERT_NULLS_FOR_MISSING_COLUMNS(false),
+
+        /**
+         * Feature that enables coercing an empty {@link String} to `null`
+         *
+         * Feature is disabled by default
+         */
+        EMPTY_STRING_AS_NULL(false)
         ;
 
         final boolean _defaultState;
@@ -1056,6 +1063,9 @@ public String getText() throws IOException {
         if (_currToken == JsonToken.FIELD_NAME) {
             return _currentName;
         }
+        if (_currentValue.equals("")) {
+            return isEnabled(CsvParser.Feature.EMPTY_STRING_AS_NULL) ? null : _currentValue;
+        }
         return _currentValue;
     }
 

csv/src/test/java/com/fasterxml/jackson/dataformat/csv/deser/EmptyStringAsNullTest.java

@@ -0,0 +1,65 @@
+package com.fasterxml.jackson.dataformat.csv.deser;
+
+import com.fasterxml.jackson.annotation.JsonPropertyOrder;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectReader;
+import com.fasterxml.jackson.dataformat.csv.CsvMapper;
+import com.fasterxml.jackson.dataformat.csv.CsvParser;
+import org.junit.Test;
+
+import java.io.IOException;
+
+import static org.junit.Assert.*;
+
+/**
+ * Test for {@link CsvParser.Feature#EMPTY_STRING_AS_NULL}
+ */
+public class EmptyStringAsNullTest {
+
+
+    @JsonPropertyOrder({"firstName", "middleName", "lastName"})
+    static class TestUser {
+        public String firstName, middleName, lastName;
+    }
+
+    @Test
+    public void givenFeatureDisabledByDefault_whenColumnIsEmptyString_thenParseAsEmptyString() throws IOException {
+        // setup test data
+        TestUser expectedTestUser = new TestUser();
+        expectedTestUser.firstName = "Grace";
+        expectedTestUser.middleName = "";
+        expectedTestUser.lastName = "Hopper";
+        CsvMapper csvMapper = CsvMapper.builder().build();
+        ObjectReader objectReader = csvMapper.readerFor(TestUser.class).with(csvMapper.schemaFor(TestUser.class));
+        String csv = "Grace,,Hopper";
+
+        // execute
+        TestUser actualTestUser = objectReader.readValue(csv);
+
+        // test
+        assertNotNull(actualTestUser);
+        assertEquals(expectedTestUser.firstName, actualTestUser.firstName);
+        assertEquals(expectedTestUser.middleName, actualTestUser.middleName);
+        assertEquals(expectedTestUser.lastName, actualTestUser.lastName);
+    }
+
+    @Test
+    public void givenFeatureEnabled_whenColumnIsEmptyString_thenParseAsNull() throws IOException {
+        // setup test data
+        TestUser expectedTestUser = new TestUser();
+        expectedTestUser.firstName = "Grace";
+        expectedTestUser.lastName = "Hopper";
+        CsvMapper csvMapper = CsvMapper.builder().enable(CsvParser.Feature.EMPTY_STRING_AS_NULL).build();
+        ObjectReader objectReader = csvMapper.readerFor(TestUser.class).with(csvMapper.schemaFor(TestUser.class));
+        String csv = "Grace,,Hopper";
+
+        // execute
+        TestUser actualTestUser = objectReader.readValue(csv);
+
+        // test
+        assertNotNull(actualTestUser);
+        assertEquals(expectedTestUser.firstName, actualTestUser.firstName);
+        assertNull("The column that contains an empty String should be deserialized as null ", actualTestUser.middleName);
+        assertEquals(expectedTestUser.lastName, actualTestUser.lastName);
+    }
+}