Posted feedback without "result" cause NPE in DDI API (#399)

* Fix for the bug by using @Valid on member variables

- add junit test
- done some refactoring

Signed-off-by: Jonathan Philip Knoblauch <JonathanPhilip.Knoblauch@bosch-si.com>

* Refactoring of junit tests

Signed-off-by: Jonathan Philip Knoblauch <JonathanPhilip.Knoblauch@bosch-si.com>

hawkbit-ddi-api/src/main/java/org/eclipse/hawkbit/ddi/json/model/DdiActionFeedback.java

@@ -8,6 +8,7 @@
  */
 package org.eclipse.hawkbit.ddi.json.model;
 
+import javax.validation.Valid;
 import javax.validation.constraints.NotNull;
 
 import com.fasterxml.jackson.annotation.JsonCreator;
@@ -40,6 +41,7 @@ public class DdiActionFeedback {
     private final String time;
 
     @NotNull
+    @Valid
     private final DdiStatus status;
 
     /**

hawkbit-ddi-api/src/main/java/org/eclipse/hawkbit/ddi/json/model/DdiResult.java

@@ -8,7 +8,8 @@
  */
 package org.eclipse.hawkbit.ddi.json.model;
 
-import org.hibernate.validator.constraints.NotEmpty;
+import javax.validation.Valid;
+import javax.validation.constraints.NotNull;
 
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
@@ -20,7 +21,8 @@ import com.fasterxml.jackson.annotation.JsonValue;
  */
 public class DdiResult {
 
-    @NotEmpty
+    @NotNull
+    @Valid
     private final FinalResult finished;
 
     private final DdiProgress progress;

hawkbit-ddi-api/src/main/java/org/eclipse/hawkbit/ddi/json/model/DdiStatus.java

@@ -11,6 +11,7 @@ package org.eclipse.hawkbit.ddi.json.model;
 import java.util.Collections;
 import java.util.List;
 
+import javax.validation.Valid;
 import javax.validation.constraints.NotNull;
 
 import com.fasterxml.jackson.annotation.JsonCreator;
@@ -23,9 +24,11 @@ import com.fasterxml.jackson.annotation.JsonValue;
 public class DdiStatus {
 
     @NotNull
+    @Valid
     private final ExecutionStatus execution;
 
     @NotNull
+    @Valid
     private final DdiResult result;
 
     private final List<String> details;
@@ -60,8 +63,8 @@ public class DdiStatus {
     public List<String> getDetails() {
         if (details == null) {
             return Collections.emptyList();
-        }        
-        
+        }
+
         return Collections.unmodifiableList(details);
     }