@Override
    public Object put( String key , Object v ){
        if ( key == null )
            throw new RuntimeException( "key should never be null" );
        else if ( key.equals( "_id" ) )
            _id = v;
        else if ( key.equals( "filename" ) )
            _filename = v == null ? null : v.toString();
        else if ( key.equals( "contentType" ) )
            _contentType = (String)v;
        else if ( key.equals( "length" ) )
            _length = ((Number)v).longValue();
        else if ( key.equals( "chunkSize" ) )
            _chunkSize = ((Number)v).longValue();
        else if ( key.equals( "uploadDate" ) )
            _uploadDate = (Date)v;
        else if ( key.equals( "md5" ) )
            _md5 = (String)v;
        else
            _extradata.put( key , v );
        return v;
    }