code: void makePackageDoc(PackageSymbol pack, TreePath treePath) {
          PackageDocImpl result = packageMap.get(pack);
          if (result != null) {
              if (treePath != null) result.setTreePath(treePath);
          } else {
              result = new PackageDocImpl(this, pack, treePath);
              packageMap.put(pack, result);
          }
      }
docs: Create the PackageDoc (or a subtype) for a package symbol.