Added support for PropertyIsNull filter.

Added a simple comparison and read/write for PropertyIsNull
encoded as XML including tests for each.

lib/OpenLayers/Filter/Comparison.js

@@ -27,6 +27,7 @@ OpenLayers.Filter.Comparison = OpenLayers.Class(OpenLayers.Filter, {
      * - OpenLayers.Filter.Comparison.GREATER_THAN_OR_EQUAL_TO = ">=";
      * - OpenLayers.Filter.Comparison.BETWEEN                  = "..";
      * - OpenLayers.Filter.Comparison.LIKE                     = "~";
+     * - OpenLayers.Filter.Comparison.IS_NULL                  = "NULL";
      */
     type: null,
     
@@ -154,6 +155,10 @@ OpenLayers.Filter.Comparison = OpenLayers.Class(OpenLayers.Filter, {
                 var regexp = new RegExp(this.value, "gi");
                 result = regexp.test(got);
                 break;
+            case OpenLayers.Filter.Comparison.IS_NULL:
+                var got = context[this.property];
+                result = (got === null || got === undefined);
+                break;
         }
         return result;
     },
@@ -260,3 +265,4 @@ OpenLayers.Filter.Comparison.LESS_THAN_OR_EQUAL_TO    = "<=";
 OpenLayers.Filter.Comparison.GREATER_THAN_OR_EQUAL_TO = ">=";
 OpenLayers.Filter.Comparison.BETWEEN                  = "..";
 OpenLayers.Filter.Comparison.LIKE                     = "~";
+OpenLayers.Filter.Comparison.IS_NULL                  = "NULL";

lib/OpenLayers/Format/Filter/v1.js

@@ -212,6 +212,13 @@ OpenLayers.Format.Filter.v1 = OpenLayers.Class(OpenLayers.Format.XML, {
             "Function": function(node, obj) {
                 //TODO write decoder for it
                 return;
+            },
+            "PropertyIsNull": function(node, obj) {
+                var filter = new OpenLayers.Filter.Comparison({
+                    type: OpenLayers.Filter.Comparison.IS_NULL
+                });
+                this.readChildNodes(node, filter);
+                obj.filters.push(filter);
             }
         }
     },
@@ -448,6 +455,11 @@ OpenLayers.Format.Filter.v1 = OpenLayers.Class(OpenLayers.Format.XML, {
                     this.writeOgcExpression(params[i], node);
                 }
                 return node;
+            },
+            "PropertyIsNull": function(filter) {
+                var node = this.createElementNSPlus("ogc:PropertyIsNull");
+                this.writeNode("PropertyName", filter, node);
+                return node;
             }
         }
     },
@@ -480,6 +492,7 @@ OpenLayers.Format.Filter.v1 = OpenLayers.Class(OpenLayers.Format.XML, {
         ">=": "PropertyIsGreaterThanOrEqualTo",
         "..": "PropertyIsBetween",
         "~": "PropertyIsLike",
+        "NULL": "PropertyIsNull",
         "BBOX": "BBOX",
         "DWITHIN": "DWITHIN",
         "WITHIN": "WITHIN",

tests/Filter/Comparison.html

@@ -164,6 +164,34 @@
             }),
             context: {prop: "FOO"},
             expect: false
+        }, {
+            filter: new OpenLayers.Filter.Comparison({
+                type: OpenLayers.Filter.Comparison.IS_NULL,
+                property: "prop"
+            }),
+            context: {prop: null},
+            expect: true
+        }, {
+            filter: new OpenLayers.Filter.Comparison({
+                type: OpenLayers.Filter.Comparison.IS_NULL,
+                property: "prop"
+            }),
+            context: {prop: undefined},
+            expect: true
+        }, {
+            filter: new OpenLayers.Filter.Comparison({
+                type: OpenLayers.Filter.Comparison.IS_NULL,
+                property: "prop"
+            }),
+            context: {prop: "foo"},
+            expect: false
+        }, {
+            filter: new OpenLayers.Filter.Comparison({
+                type: OpenLayers.Filter.Comparison.IS_NULL,
+                property: "prop"
+            }),
+            context: {prop: 0},
+            expect: false
         }];
         
         t.plan(cases.length);

tests/Format/Filter/v1.html

@@ -51,6 +51,44 @@
              "[1] record correct upper boundary value");
     }
 
+    function test_PropertyIsNull(t) {
+
+        t.plan(6);
+
+        var test_xml, format, xml;
+
+        format = new OpenLayers.Format.Filter.v1();
+        xml = new OpenLayers.Format.XML();
+
+        test_xml =
+            '<ogc:Filter xmlns:ogc="http://www.opengis.net/ogc">' +
+                '<ogc:PropertyIsNull>' +
+                    '<ogc:PropertyName>prop</ogc:PropertyName>' +
+                '</ogc:PropertyIsNull>' +
+            '</ogc:Filter>';
+
+        var filter = format.read(xml.read(test_xml).documentElement);
+        t.eq(filter.type, OpenLayers.Filter.Comparison.IS_NULL,
+             "[0] read correct type");
+        console.log(filter);
+        t.eq(filter.property, 'prop',
+             "[0] record correct property name");
+
+        var filter = new OpenLayers.Filter.Comparison({
+            type: OpenLayers.Filter.Comparison.IS_NULL,
+            property: "prop"
+        });
+        element = format.write(filter);
+        t.eq(element.firstChild.nodeName, 'ogc:PropertyIsNull',
+            "[1] write correct filter node name");
+        t.eq(element.firstChild.childNodes.length, 1,
+            "[1] write correct number of filter arguments");
+        t.eq(element.firstChild.firstChild.nodeName, 'ogc:PropertyName',
+            "[1] write correct filter argument name");
+        t.eq(element.firstChild.firstChild.textContent, 'prop',
+            "[1] write correct filter argument value");
+
+    }
 
     function test_Intersects(t) {