Fix syntax and private functions return values for OWS format

src/ol/format/owscapabilitiesformat.js

@@ -90,6 +90,9 @@ ol.format.OWSCapabilities.readConstraint_ = function(node, objectStack) {
   var value = ol.xml.pushParseAndPop({},
       ol.format.OWSCapabilities.CONSTRAINT_PARSERS_, node,
       objectStack);
+  if (!goog.isDef(value)) {
+    return undefined;
+  }
   if (!goog.isDef(object.constraints)) {
     object.constraints = {};
   }
@@ -140,11 +143,15 @@ ol.format.OWSCapabilities.readGet_ = function(node, objectStack) {
   goog.asserts.assert(goog.isObject(object));
   var value = ol.xml.pushParseAndPop({'url': url},
       ol.format.OWSCapabilities.REQUEST_METHOD_PARSERS_, node, objectStack);
-  if (!goog.isDef(object.get)) {
+  if (!goog.isDef(value)) {
+    return undefined;
+  }
+  var get = goog.object.get(object, 'get');
+  if (!goog.isDef(get)) {
     goog.object.set(object, 'get', [value]);
   }else {
-    goog.asserts.assert(goog.isArray(object.get));
-    object.get.push(value);
+    goog.asserts.assert(goog.isArray(get));
+    get.push(value);
   }
 
 };
@@ -176,6 +183,9 @@ ol.format.OWSCapabilities.readOperation_ = function(node, objectStack) {
   var name = node.getAttribute('name');
   var value = ol.xml.pushParseAndPop({},
       ol.format.OWSCapabilities.OPERATION_PARSERS_, node, objectStack);
+  if (!goog.isDef(value)) {
+    return undefined;
+  }
   var object = /** @type {Object} */
       (objectStack[objectStack.length - 1]);
   goog.asserts.assert(goog.isObject(object));
@@ -271,7 +281,10 @@ ol.format.OWSCapabilities.readValue_ = function(node, objectStack) {
   goog.asserts.assert(node.localName == 'Value');
   var object = objectStack[objectStack.length - 1];
   goog.asserts.assert(goog.isObject(object));
-  var key = /** @type {string} */ (ol.format.XSD.readString(node));
+  var key = ol.format.XSD.readString(node);
+  if (!goog.isDef(key)) {
+    return undefined;
+  }
   goog.object.set(object, key, true);
 };
 
@@ -303,8 +316,7 @@ ol.format.OWSCapabilities.PARSERS_ = ol.xml.makeParsersNS(
       'OperationsMetadata': ol.xml.makeObjectPropertySetter(
           ol.format.OWSCapabilities.readOperationsMetadata_,
           'operationsMetadata')
-    }
-    );
+    });
 
 
 /**