Merge pull request FasterXML#149 from evanj/master

JsonParser, ObjectCodec: javadoc: empty docs to return null

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/core/JsonParser.java

@@ -1390,7 +1390,9 @@ public <T> Iterator<T> readValuesAs(TypeReference<?> valueTypeRef) throws IOExce
      * represented by root {@link TreeNode} of resulting model.
      * For JSON Arrays it will an array node (with child nodes),
      * for objects object node (with child nodes), and for other types
-     * matching leaf node type
+     * matching leaf node type. Empty or whitespace documents are null.
+     *
+     * @return root of the document, or null if empty or whitespace.
      */
     @SuppressWarnings("unchecked")
     public <T extends TreeNode> T readValueAsTree() throws IOException {

src/main/java/com/fasterxml/jackson/core/ObjectCodec.java

@@ -113,7 +113,10 @@ public abstract void writeValue(JsonGenerator jgen, Object value)
      * using set of {@link TreeNode} instances. Returns
      * root of the resulting tree (where root can consist
      * of just a single node if the current event is a
-     * value event, not container).
+     * value event, not container). Empty or whitespace
+     * documents return null.
+     *
+     * @return next tree from jp, or null if empty.
      */
     @Override
     public abstract <T extends TreeNode> T readTree(JsonParser jp)