diff --git a/core/src/main/java/org/apache/brooklyn/core/objs/ConstraintSerialization.java b/core/src/main/java/org/apache/brooklyn/core/objs/ConstraintSerialization.java
index 984e2e7127..32b71f0461 100644
--- a/core/src/main/java/org/apache/brooklyn/core/objs/ConstraintSerialization.java
+++ b/core/src/main/java/org/apache/brooklyn/core/objs/ConstraintSerialization.java
@@ -167,12 +167,13 @@ public void add(ConstraintSerialization constraintSerialization) {
     @SuppressWarnings({ "unchecked", "rawtypes" })
     private void init() {
         PredicateSerializationRuleAdder.predicateListConstructor((o) -> ConfigConstraints.required()).
-            equivalentPredicates(Predicates.notNull(), StringPredicates.isNonBlank()).add(this);
+            equivalentPredicates(StringPredicates.isNonBlank()).add(this);
 
         PredicateSerializationRuleAdder.predicateListConstructor((o) -> Predicates.or((Iterable)o)).preferredName("any").equivalentNames("or").add(this);
         PredicateSerializationRuleAdder.predicateListConstructor((o) -> /* and predicate is default when given list */ toPredicateFromJson(o)).preferredName("all").sample(Predicates.and(Collections.emptyList())).equivalentNames("and").add(this);
         PredicateSerializationRuleAdder.noArgConstructor(Predicates::alwaysFalse).add(this);
         PredicateSerializationRuleAdder.noArgConstructor(Predicates::alwaysTrue).add(this);
+        PredicateSerializationRuleAdder.noArgConstructor(Predicates::notNull).add(this);
         
         PredicateSerializationRuleAdder.noArgConstructor(ResourcePredicates::urlExists).preferredName("urlExists").add(this);
         PredicateSerializationRuleAdder.noArgConstructor(StringPredicates::isBlank).add(this);
diff --git a/core/src/test/java/org/apache/brooklyn/core/objs/BasicSpecParameterFromListTest.java b/core/src/test/java/org/apache/brooklyn/core/objs/BasicSpecParameterFromListTest.java
index 887e054980..3ce8d9c14c 100644
--- a/core/src/test/java/org/apache/brooklyn/core/objs/BasicSpecParameterFromListTest.java
+++ b/core/src/test/java/org/apache/brooklyn/core/objs/BasicSpecParameterFromListTest.java
@@ -28,6 +28,7 @@
 import org.apache.brooklyn.api.mgmt.classloading.BrooklynClassLoadingContext;
 import org.apache.brooklyn.api.objs.SpecParameter;
 import org.apache.brooklyn.config.ConfigKey;
+import org.apache.brooklyn.core.config.ConfigConstraints;
 import org.apache.brooklyn.core.mgmt.classloading.JavaBrooklynClassLoadingContext;
 import org.apache.brooklyn.core.test.BrooklynMgmtUnitTestSupport;
 import org.apache.brooklyn.util.text.StringPredicates;
@@ -99,7 +100,7 @@ public void testFullDefinition() {
         assertEquals(type.getDefaultValue(), defaultValue);
         assertEquals(type.getDescription(), description);
         assertTrue(type.getInheritanceByContext().values().isEmpty(), "Unexpected inheritance: "+type.getInheritanceByContext());
-        assertConstraint(type.getConstraint(), StringPredicates.isNonBlank());
+        assertConstraint(type.getConstraint(), ConfigConstraints.required());
     }
 
     @Test
@@ -132,7 +133,7 @@ public void testConstraintAsArray() {
                 "name", name,
                 "constraints", ImmutableList.of(constraint)));
         ConfigKey<?> type = input.getConfigKey();
-        assertConstraint(type.getConstraint(), StringPredicates.isNonBlank());
+        assertConstraint(type.getConstraint(), ConfigConstraints.required());
     }
 
     @Test(expectedExceptions = IllegalArgumentException.class)
diff --git a/core/src/test/java/org/apache/brooklyn/core/objs/ConstraintSerializationTest.java b/core/src/test/java/org/apache/brooklyn/core/objs/ConstraintSerializationTest.java
index a8fdb0260b..bdbc5adc2c 100644
--- a/core/src/test/java/org/apache/brooklyn/core/objs/ConstraintSerializationTest.java
+++ b/core/src/test/java/org/apache/brooklyn/core/objs/ConstraintSerializationTest.java
@@ -86,7 +86,7 @@ public void testAcceptsString() {
     
     @Test
     public void testAltPred() {
-        Predicate<?> p = Predicates.notNull();
+        Predicate<?> p = StringPredicates.isNonBlank();
         Assert.assertEquals(ConstraintSerialization.INSTANCE.toJsonList(p),
             MutableList.of("required"));
         assertSamePredicate(ConstraintSerialization.INSTANCE.toPredicateFromJson("required"),