Add default JDBCType.NULL for null values.

Signed-off-by: Sergey Korotaev <sergey.evgen.kor2501@gmail.com>

Original pull request #2068
Closes #1935

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/SqlParametersFactory.java

@@ -15,6 +15,7 @@
  */
 package org.springframework.data.jdbc.core.convert;
 
+import java.sql.JDBCType;
 import java.sql.SQLType;
 import java.util.ArrayList;
 import java.util.List;
@@ -41,6 +42,7 @@ import org.springframework.util.Assert;
  * @author Jens Schauder
  * @author Chirag Tailor
  * @author Mikhail Polivakha
+ * @author Sergey Korotaev
  * @since 2.4
  */
 public class SqlParametersFactory {
@@ -187,11 +189,9 @@ public class SqlParametersFactory {
 	private void addConvertedValue(SqlIdentifierParameterSource parameterSource, @Nullable Object value,
 			SqlIdentifier paramName, Class<?> javaType, SQLType sqlType) {
 
-		JdbcValue jdbcValue = converter.writeJdbcValue( //
-				value, //
-				javaType, //
-				sqlType //
-		);
+		JdbcValue jdbcValue = value != null
+				? converter.writeJdbcValue(value, javaType, sqlType)
+				: JdbcValue.of(null, JDBCType.NULL);
 
 		parameterSource.addValue( //
 				paramName, //

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/core/convert/SqlParametersFactoryTest.java

@@ -21,6 +21,7 @@ import static org.assertj.core.api.Assertions.*;
 import static org.mockito.Mockito.*;
 import static org.springframework.data.jdbc.core.convert.DefaultDataAccessStrategyUnitTests.*;
 
+import java.sql.JDBCType;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
@@ -32,6 +33,7 @@ import org.springframework.data.annotation.Id;
 import org.springframework.data.convert.ReadingConverter;
 import org.springframework.data.convert.WritingConverter;
 import org.springframework.data.jdbc.core.mapping.JdbcMappingContext;
+import org.springframework.data.jdbc.core.mapping.JdbcValue;
 import org.springframework.data.relational.core.conversion.IdValueSource;
 import org.springframework.data.relational.core.mapping.Column;
 import org.springframework.data.relational.core.mapping.RelationalMappingContext;
@@ -42,6 +44,7 @@ import org.springframework.jdbc.core.JdbcOperations;
  * Unit tests for {@link SqlParametersFactory}.
  *
  * @author Chirag Tailor
+ * @author Sergey Korotaev
  */
 class SqlParametersFactoryTest {
 
@@ -162,6 +165,69 @@ class SqlParametersFactoryTest {
 		assertThat(sqlParameterSource.getValue("val&ue")).isNull();
 	}
 
+	@Test
+	// GH-1935
+	void enumParameterIsNotNullReturnCorrectSqlTypeFromConverter() {
+
+		WithEnumEntity entity = new WithEnumEntity(23L, DummyEnum.ONE);
+
+		SqlParametersFactory sqlParametersFactory = createSqlParametersFactoryWithConverters(
+				singletonList(WritingEnumConverter.INSTANCE));
+
+		SqlIdentifierParameterSource sqlParameterSource = sqlParametersFactory.forInsert(entity,
+				WithEnumEntity.class, Identifier.empty(), IdValueSource.PROVIDED);
+
+		assertThat(sqlParameterSource.getValue("id")).isEqualTo(23L);
+		assertThat(sqlParameterSource.getValue("dummy_enum")).isEqualTo(DummyEnum.ONE.name());
+		assertThat(sqlParameterSource.getSqlType("dummy_enum")).isEqualTo(1111);
+	}
+
+	@Test
+	// GH-1935
+	void enumParameterIsNullReturnCorrectSqlTypeFromConverter() {
+		WithEnumEntity entity = new WithEnumEntity(23L, null);
+
+		SqlParametersFactory sqlParametersFactory = createSqlParametersFactoryWithConverters(
+				singletonList(WritingEnumConverter.INSTANCE));
+
+		SqlIdentifierParameterSource sqlParameterSource = sqlParametersFactory.forInsert(entity,
+				WithEnumEntity.class, Identifier.empty(), IdValueSource.PROVIDED);
+
+		assertThat(sqlParameterSource.getValue("id")).isEqualTo(23L);
+		assertThat(sqlParameterSource.getSqlType("dummy_enum")).isEqualTo(JDBCType.NULL.getVendorTypeNumber());
+		assertThat(sqlParameterSource.getValue("dummy_enum")).isNull();
+	}
+
+	@Test
+	// GH-1935
+	void enumParameterIsNotNullReturnCorrectSqlTypeWithoutConverter() {
+
+		WithEnumEntity entity = new WithEnumEntity(23L, DummyEnum.ONE);
+
+		SqlIdentifierParameterSource sqlParameterSource = sqlParametersFactory.forInsert(entity,
+				WithEnumEntity.class, Identifier.empty(), IdValueSource.PROVIDED);
+
+		assertThat(sqlParameterSource.getValue("id")).isEqualTo(23L);
+		assertThat(sqlParameterSource.getValue("dummy_enum")).isEqualTo(DummyEnum.ONE.name());
+		assertThat(sqlParameterSource.getSqlType("dummy_enum")).isEqualTo(12);
+
+	}
+
+	@Test
+	// GH-1935
+	void enumParameterIsNullReturnCorrectSqlTypeWithoutConverter() {
+
+		WithEnumEntity entity = new WithEnumEntity(23L, null);
+
+		SqlIdentifierParameterSource sqlParameterSource = sqlParametersFactory.forInsert(entity,
+				WithEnumEntity.class, Identifier.empty(), IdValueSource.PROVIDED);
+
+		assertThat(sqlParameterSource.getValue("id")).isEqualTo(23L);
+		assertThat(sqlParameterSource.getSqlType("dummy_enum")).isEqualTo(JDBCType.NULL.getVendorTypeNumber());
+		assertThat(sqlParameterSource.getValue("dummy_enum")).isNull();
+
+	}
+
 	@WritingConverter
 	enum IdValueToStringConverter implements Converter<IdValue, String> {
 
@@ -229,6 +295,17 @@ class SqlParametersFactoryTest {
 		}
 	}
 
+	@WritingConverter
+	enum WritingEnumConverter implements Converter<DummyEnum, JdbcValue> {
+
+		INSTANCE;
+
+		@Override
+		public JdbcValue convert(DummyEnum source) {
+			return JdbcValue.of(source.name().toUpperCase(), JDBCType.OTHER);
+		}
+	}
+
 	@WritingConverter
 	enum BooleanToStringConverter implements Converter<Boolean, String> {
 
@@ -295,6 +372,21 @@ class SqlParametersFactoryTest {
 		}
 	}
 
+	private static class WithEnumEntity {
+		@Id Long id;
+
+		DummyEnum dummyEnum;
+
+		public WithEnumEntity(Long id, DummyEnum dummyEnum) {
+			this.id = id;
+			this.dummyEnum = dummyEnum;
+		}
+	}
+
+	private enum DummyEnum {
+		ONE, TWO
+	}
+
 	private SqlParametersFactory createSqlParametersFactoryWithConverters(List<?> converters) {
 
 		MappingJdbcConverter converter = new MappingJdbcConverter(context, relationResolver,