Allow null elements in Document#getList (#1066)

JAVA-4837

Author: jyemin

bson/src/main/org/bson/Document.java

@@ -392,17 +392,17 @@ public <T> List<T> getList(final Object key, final Class<T> clazz, final List<T>
     // A ClassCastException will be thrown if an element in the list is not of type T.
     @SuppressWarnings("unchecked")
     private <T> List<T> constructValuesList(final Object key, final Class<T> clazz, final List<T> defaultValue) {
-        List<?> value = get(key, List.class);
+        List<T> value = get(key, List.class);
         if (value == null) {
             return defaultValue;
         }
 
         for (Object item : value) {
-            if (!clazz.isAssignableFrom(item.getClass())) {
+            if (item != null && !clazz.isAssignableFrom(item.getClass())) {
                 throw new ClassCastException(format("List element cannot be cast to %s", clazz.getName()));
             }
         }
-        return (List<T>) value;
+        return value;
     }
 
     /**

bson/src/test/unit/org/bson/types/DocumentSpecification.groovy

@@ -69,6 +69,7 @@ class DocumentSpecification extends Specification {
         when:
         Document doc = Document.parse("{x: 1, y: ['two', 'three'], z: [{a: 'one'}, {b:2}], w: {a: ['One', 'Two']}}")
                 .append('numberList', [10, 20.5d, 30L])
+                .append('listWithNullElement', [10, null, 20])
         List<String> defaultList = ['a', 'b', 'c']
 
         then:
@@ -84,6 +85,9 @@ class DocumentSpecification extends Specification {
         doc.getList('numberList', Number).get(0) == 10
         doc.getList('numberList', Number).get(1) == 20.5d
         doc.getList('numberList', Number).get(2) == 30L
+        doc.getList('listWithNullElement', Number).get(0) == 10
+        doc.getList('listWithNullElement', Number).get(1) == null
+        doc.getList('listWithNullElement', Number).get(2) == 20
     }
 
     def 'should return null list when key is not found'() {
@@ -103,6 +107,7 @@ class DocumentSpecification extends Specification {
         doc.getList('a', String, defaultList) == defaultList
     }
 
+
     def 'should throw an exception when the list elements are not objects of the specified class'() {
         given:
         Document doc = Document.parse('{x: 1, y: [{a: 1}, {b: 2}], z: [1, 2]}')