for now, make give all users the role of a HOSTMASTER

src/test/java/org/hostsharing/hsadminng/service/accessfilter/JSonBuilder.java

@@ -21,7 +21,7 @@ public class JSonBuilder {
     }
 
     private static String inQuotes(Object value) {
-        return "\"" + value.toString() + "\"";
+        return value != null ? "\"" + value.toString() + "\"" : "null";
     }
 
 }

src/test/java/org/hostsharing/hsadminng/service/accessfilter/JSonDeserializerWithAccessFilterUnitTest.java

@@ -72,6 +72,20 @@ public class JSonDeserializerWithAccessFilterUnitTest {
         given(jsonParser.getCodec()).willReturn(codec);
     }
 
+    @Test
+    public void shouldDeserializeNullField() throws IOException {
+        // given
+        givenJSonTree(asJSon(
+            ImmutablePair.of("id", 1234L),
+            ImmutablePair.of("openStringField", null)));
+
+        // when
+        GivenDto actualDto = new JSonDeserializerWithAccessFilter<>(ctx, jsonParser, null, GivenDto.class).deserialize();
+
+        // then
+        assertThat(actualDto.openStringField).isNull();
+    }
+
     @Test
     public void shouldDeserializeStringField() throws IOException {
         // given