#2199 - ScalarTypeWrapper doesn't handle "nullValue" correctly

Fix for - standard JPA AttributeConverter which doesn't have the getNullValue method, he/she can't convert null to a custom null object

AttributeConverterAdapter probes the AttributeConverter for the nullValue rather than just assuming it is null.

ebean-core/src/main/java/io/ebeaninternal/server/type/AttributeConverterAdapter.java

@@ -10,14 +10,24 @@ import javax.persistence.AttributeConverter;
 class AttributeConverterAdapter<B,S> implements ScalarTypeConverter<B, S> {
 
   private final AttributeConverter<B,S> converter;
+  private final B nullValue;
 
   AttributeConverterAdapter(AttributeConverter<B, S> converter) {
     this.converter = converter;
+    this.nullValue = probeNullValue();
+  }
+
+  private B probeNullValue() {
+    try {
+      return converter.convertToEntityAttribute(null);
+    } catch (Exception e) {
+      return null;
+    }
   }
 
   @Override
   public B getNullValue() {
-    return null;
+    return nullValue;
   }
 
   @Override

ebean-core/src/test/java/io/ebeaninternal/server/type/ScalarTypeWrapperAdapterTest.java

@@ -0,0 +1,62 @@
+package io.ebeaninternal.server.type;
+
+import org.junit.Test;
+
+import javax.persistence.AttributeConverter;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+
+@SuppressWarnings({"rawtypes", "unchecked"})
+public class ScalarTypeWrapperAdapterTest {
+
+  private final ScalarTypeString stringType = ScalarTypeString.INSTANCE;
+  private final MyAdapter myAdapter = new MyAdapter();
+  private final AttributeConverterAdapter converterAdapter = new AttributeConverterAdapter(myAdapter);
+  private final ScalarTypeWrapper<Long, String> wrapper = new ScalarTypeWrapper(Long.class, stringType, converterAdapter);
+
+  @Test
+  public void toJdbcType() {
+    assertThat(wrapper.toJdbcType(42L)).isEqualTo("L42");
+    assertThat(wrapper.toJdbcType(93L)).isEqualTo("L93");
+  }
+
+  @Test
+  public void toJdbcType_when_nullValue() {
+    assertThat(wrapper.toJdbcType(MyAdapter.NULL_VAL)).isNull();
+  }
+
+  @Test
+  public void toBeanType_when_null_expect_customNullValue() {
+    assertThat(wrapper.toBeanType(null)).isEqualTo(MyAdapter.NULL_VAL);
+  }
+
+  @Test
+  public void toBeanType() {
+    assertThat(wrapper.toBeanType("L34")).isEqualTo(34L);
+  }
+
+  /**
+   * An AttributeConverter with a custom null value (of -1L).
+   */
+  private static class MyAdapter implements AttributeConverter<Long, String> {
+
+    private static final Long NULL_VAL = -1L;
+
+    @Override
+    public String convertToDatabaseColumn(Long val) {
+      if (val == null || val.equals(NULL_VAL)) {
+        return null;
+      }
+      return "L" + val;
+    }
+
+    @Override
+    public Long convertToEntityAttribute(String dbData) {
+      if (dbData == null) {
+        return NULL_VAL;
+      }
+      return Long.parseLong(dbData.substring(1));
+    }
+  }
+}