adding violated keyword to NotSchema and NullSchema

Author: erosb

core/src/main/java/org/everit/json/schema/NotSchema.java

@@ -59,7 +59,8 @@ public void validate(final Object subject) {
     } catch (ValidationException e) {
       return;
     }
-    throw new ValidationException(this, "subject must not be valid agains schema " + mustNotMatch);
+    throw new ValidationException(this, "subject must not be valid agains schema " + mustNotMatch,
+        "not");
   }
 
 }

core/src/main/java/org/everit/json/schema/NullSchema.java

@@ -47,7 +47,7 @@ public NullSchema(final Builder builder) {
   public void validate(final Object subject) {
     if (!(subject == null || subject == JSONObject.NULL)) {
       throw new ValidationException(this, "expected: null, found: "
-          + subject.getClass().getSimpleName());
+          + subject.getClass().getSimpleName(), "type");
     }
   }
 

core/src/test/java/org/everit/json/schema/NotSchemaTest.java

@@ -22,7 +22,10 @@ public class NotSchemaTest {
   @Test
   public void failure() {
     NotSchema subject = NotSchema.builder().mustNotMatch(BooleanSchema.INSTANCE).build();
-    TestSupport.expectFailure(subject, true);
+    TestSupport.failureOf(subject)
+        .input(true)
+        .expectedKeyword("not")
+        .expect();
   }
 
   @Test

core/src/test/java/org/everit/json/schema/NullSchemaTest.java

@@ -22,7 +22,10 @@ public class NullSchemaTest {
 
   @Test
   public void failure() {
-    TestSupport.expectFailure(NullSchema.INSTANCE, "null");
+    TestSupport.failureOf(NullSchema.INSTANCE)
+        .expectedKeyword("type")
+        .input("null")
+        .expect();
   }
 
   @Test