private String nextString() {
                ByteBuffer nextBuffer = responseData.read();
                if (nextBuffer == null) return null; // end of transmission
                return Charset.forName("utf-8").decode(nextBuffer).toString();
            }
Convenience which returns the next piece of content from the response data of this as a string, or
null if there is no more data. The channel must always be consumed until there is no more data.
container-core/src/test/java/com/yahoo/processing/processors/MockUserDatabaseClient.java