title: folder.getSheets() returning null?
body: <p>I'm trying to go through and entire workspace and list each element in a treeview, but when I attempt to grab the sheets in the found folders the getSheets() method in the Folder class always returns null. Am I doing something wrong?</p>
  
  <pre><code>    TreeItem&lt;String&gt; workspace = new TreeItem&lt;&gt;("Earls Workspace", workspaceIcon);
      workspace.setExpanded(true);
  
      try {
          Workspace earlsWorkspace = SmartsheetConnector.getInstance().getSmartsheet().workspaces().getWorkspace(*****);
          List&lt;Sheet&gt; sheets = earlsWorkspace.getSheets();
          List&lt;Folder&gt; folders = earlsWorkspace.getFolders();
  
          for (Folder folder : folders) {
              TreeItem&lt;String&gt; item = new TreeItem&lt;&gt;(folder.getName(), new ImageView(folderIcon));
              System.out.println("Folder: " + folder.getName());
              List&lt;Sheet&gt; folderSheets = folder.getSheets(); &lt;- problem is here
              System.out.println(folderSheets.toArray());
              for (Sheet sheet : folderSheets) {
                  TreeItem&lt;String&gt; subItem = new TreeItem&lt;&gt;(sheet.getName(), new ImageView(sheetIcon));
                  item.getChildren().add(subItem);
              }
  
              workspace.getChildren().add(item);
          }
  
          for (Sheet sheet : sheets) {
              TreeItem&lt;String&gt; item = new TreeItem&lt;&gt;(sheet.getName(), new ImageView(sheetIcon));
              workspace.getChildren().add(item);
          }
  
          sheetExplorer.setRoot(workspace);
      } catch (SmartsheetException ex) {
          ex.printStackTrace();
      }
  </code></pre>
  
  <p>I've purposefully blocked out the workspace ID.</p>