void makeFieldDoc(VarSymbol var, String docComment, JCVariableDecl tree, Position.LineMap lineMap) {
        FieldDocImpl result = fieldMap.get(var);
        if (result != null) {
            if (docComment != null) result.setRawCommentText(docComment);
            if (tree != null) result.setTree(tree);
        } else {
            result = new FieldDocImpl(this, var, docComment, tree, lineMap);
            fieldMap.put(var, result);
        }
    }