change MetadataSchemaDraftDTO.abstractSchema boolean to Boolean

this fixes the following error:
"Cannot map null into type boolean (set DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES to 'false' to allow)"

Author: dennisvang

src/main/java/org/fairdatateam/fairdatapoint/api/dto/schema/MetadataSchemaDraftDTO.java

@@ -47,7 +47,7 @@ public class MetadataSchemaDraftDTO {
     @NotNull
     private String description;
 
-    private boolean abstractSchema;
+    private Boolean abstractSchema;
 
     @NotNull
     private String definition;

src/test/java/org/fairdatateam/fairdatapoint/acceptance/schema/Draft_PUT.java

@@ -103,7 +103,7 @@ public void res200() {
         assertThat(result.getBody().getName(), is(equalTo(reqDto.getName())));
         assertThat(result.getBody().getDescription(), is(equalTo(reqDto.getDescription())));
         assertThat(result.getBody().getDefinition(), is(equalTo(reqDto.getDefinition())));
-        assertThat(result.getBody().isAbstractSchema(), is(equalTo(reqDto.isAbstractSchema())));
+        assertThat(result.getBody().getAbstractSchema(), is(equalTo(reqDto.isAbstractSchema())));
         assertThat(result.getBody().getExtendsSchemaUuids(), is(equalTo(reqDto.getExtendsSchemaUuids())));
     }