=== modified file 'dhis-2/dhis-api/src/main/java/org/hisp/dhis/query/Criteria.java'
--- dhis-2/dhis-api/src/main/java/org/hisp/dhis/query/Criteria.java	2015-06-03 03:42:15 +0000
+++ dhis-2/dhis-api/src/main/java/org/hisp/dhis/query/Criteria.java	2015-06-04 09:25:32 +0000
@@ -70,8 +70,8 @@
                 continue;
             }
 
-            if ( restriction.getParameters().size() > restriction.getOperator().getMax()
-                || restriction.getParameters().size() < restriction.getOperator().getMin() )
+            if ( (restriction.getOperator().getMax() != null && restriction.getParameters().size() > restriction.getOperator().getMax())
+                || (restriction.getOperator().getMin() != null && restriction.getParameters().size() < restriction.getOperator().getMin()) )
             {
                 continue;
             }

=== modified file 'dhis-2/dhis-api/src/main/java/org/hisp/dhis/query/Operator.java'
--- dhis-2/dhis-api/src/main/java/org/hisp/dhis/query/Operator.java	2015-02-23 11:17:55 +0000
+++ dhis-2/dhis-api/src/main/java/org/hisp/dhis/query/Operator.java	2015-06-04 09:25:32 +0000
@@ -43,6 +43,7 @@
     LT( Typed.from( String.class, Boolean.class, Number.class, Date.class ), 1 ),
     GE( Typed.from( String.class, Boolean.class, Number.class, Date.class ), 1 ),
     LE( Typed.from( String.class, Boolean.class, Number.class, Date.class ), 1 ),
+    NULL( Typed.from( String.class, Boolean.class, Number.class, Date.class ) ),
     BETWEEN( Typed.from( String.class, Number.class, Date.class ), 2 ),
     LIKE( Typed.from( String.class ), 1 ),
     ILIKE( Typed.from( String.class ), 1 ),

=== modified file 'dhis-2/dhis-api/src/main/java/org/hisp/dhis/query/Restrictions.java'
--- dhis-2/dhis-api/src/main/java/org/hisp/dhis/query/Restrictions.java	2015-03-09 08:57:50 +0000
+++ dhis-2/dhis-api/src/main/java/org/hisp/dhis/query/Restrictions.java	2015-06-04 09:25:32 +0000
@@ -91,6 +91,11 @@
         return new Restriction( path, Operator.IN, values );
     }
 
+    public static Restriction isNull( String path )
+    {
+        return new Restriction( path, Operator.NULL );
+    }
+
     private Restrictions()
     {
     }

=== modified file 'dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/query/CriteriaQueryEngine.java'
--- dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/query/CriteriaQueryEngine.java	2015-06-04 01:55:31 +0000
+++ dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/query/CriteriaQueryEngine.java	2015-06-04 09:25:32 +0000
@@ -146,7 +146,12 @@
         if ( Restriction.class.isInstance( criterion ) )
         {
             Restriction restriction = (Restriction) criterion;
-            junction.add( getHibernateCriterion( schema, restriction ) );
+            Criterion hibernateCriterion = getHibernateCriterion( schema, restriction );
+
+            if ( hibernateCriterion != null )
+            {
+                junction.add( hibernateCriterion );
+            }
         }
         else if ( Junction.class.isInstance( criterion ) )
         {
@@ -175,7 +180,12 @@
         if ( Restriction.class.isInstance( criterion ) )
         {
             Restriction restriction = (Restriction) criterion;
-            criteria.add( getHibernateCriterion( schema, restriction ) );
+            Criterion hibernateCriterion = getHibernateCriterion( schema, restriction );
+
+            if ( hibernateCriterion != null )
+            {
+                criteria.add( hibernateCriterion );
+            }
         }
         else if ( Junction.class.isInstance( criterion ) )
         {
@@ -199,6 +209,7 @@
         }
     }
 
+    // TODO verify parameters length
     @SuppressWarnings( "unchecked" )
     private Criterion getHibernateCriterion( Schema schema, Restriction restriction )
     {
@@ -216,11 +227,6 @@
             parameters.add( QueryUtils.getValue( property.getKlass(), parameter ) );
         }
 
-        if ( parameters.isEmpty() )
-        {
-            return null;
-        }
-
         switch ( restriction.getOperator() )
         {
             case EQ:
@@ -268,6 +274,10 @@
 
                 return Restrictions.in( property.getFieldName(), (Collection<?>) parameters.get( 0 ) );
             }
+            case NULL:
+            {
+                return Restrictions.isNull( property.getFieldName() );
+            }
         }
 
         return null;

=== modified file 'dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/query/DefaultQueryService.java'
--- dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/query/DefaultQueryService.java	2015-06-02 04:25:37 +0000
+++ dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/query/DefaultQueryService.java	2015-06-04 09:25:32 +0000
@@ -140,7 +140,7 @@
 
         String[] split = filter.split( ":" );
 
-        if ( split.length != 3 )
+        if ( split.length < 3 )
         {
             return null;
         }
@@ -202,6 +202,10 @@
             {
                 return Restrictions.in( split[0], parseInOperator( split[2] ) );
             }
+            case "null":
+            {
+                return Restrictions.isNull( split[0] );
+            }
         }
 
         return null;

=== modified file 'dhis-2/dhis-services/dhis-service-core/src/test/java/org/hisp/dhis/query/QueryServiceTest.java'
--- dhis-2/dhis-services/dhis-service-core/src/test/java/org/hisp/dhis/query/QueryServiceTest.java	2015-06-04 05:24:23 +0000
+++ dhis-2/dhis-services/dhis-service-core/src/test/java/org/hisp/dhis/query/QueryServiceTest.java	2015-06-04 09:25:32 +0000
@@ -643,4 +643,40 @@
         assertTrue( collectionContainsUid( result.getItems(), "deabcdefghC" ) );
         assertTrue( collectionContainsUid( result.getItems(), "deabcdefghD" ) );
     }
+
+    @Test
+    public void testIsNull()
+    {
+        createDataElements();
+        Query query = Query.from( schemaService.getDynamicSchema( DataElement.class ) );
+        query.add( Restrictions.isNull( "categoryCombo" ) );
+
+        Result result = queryService.query( query );
+
+        assertEquals( 6, result.size() );
+
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghA" ) );
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghB" ) );
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghC" ) );
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghD" ) );
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghE" ) );
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghF" ) );
+    }
+
+    @Test
+    public void testIsNullUrl()
+    {
+        createDataElements();
+        Query query = queryService.getQueryFromUrl( DataElement.class, Lists.newArrayList( "categoryCombo:null" ), Lists.<Order>newArrayList() );
+        Result result = queryService.query( query );
+
+        assertEquals( 6, result.size() );
+
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghA" ) );
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghB" ) );
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghC" ) );
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghD" ) );
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghE" ) );
+        assertTrue( collectionContainsUid( result.getItems(), "deabcdefghF" ) );
+    }
 }

=== modified file 'dhis-2/dhis-services/dhis-service-dxf2/src/main/java/org/hisp/dhis/dxf2/objectfilter/Filters.java'
--- dhis-2/dhis-services/dhis-service-dxf2/src/main/java/org/hisp/dhis/dxf2/objectfilter/Filters.java	2015-06-04 01:55:31 +0000
+++ dhis-2/dhis-services/dhis-service-dxf2/src/main/java/org/hisp/dhis/dxf2/objectfilter/Filters.java	2015-06-04 09:25:32 +0000
@@ -57,6 +57,11 @@
         {
             Op op = OpFactory.create( operator );
 
+            if ( op == null )
+            {
+                return;
+            }
+
             if ( op.wantValue() )
             {
                 if ( value == null )