avoid writing 2 new lines without content

Fix the following error happening on the server side:
java.lang.NullPointerException: null
	at org.jboss.netty.handler.codec.http.HttpClientCodec$Decoder.isContentAlwaysEmpty(HttpClientCodec.java:179) ~[netty-3.9.2.Final.jar:na]
Merge pull request #781 from yanns/fixFeedableBodyGenerator

avoid writing 2 new lines without content