returning groovy issue

The Groovy documentation says that you do not need to explicitly return from executed code

I have just been troubleshooting why the following code

// XMLinject ( fm_xml ; fm_key ; fm_new )

// 10_07_21 JR

// v1.1

// replace value at key from XML value



import groovy.xml.StreamingMarkupBuilder

import groovy.xml.XmlUtil



root = new XmlSlurper().parseText(fm_xml)

root.setProperty(fm_key, fm_new)

result = XmlUtil.serialize(new StreamingMarkupBuilder().bind { mkp.yield root })

//return XmlUtil.serialize(new StreamingMarkupBuilder().bind { mkp.yield root })

works with either of the last two lines enables in the Scriptmaster file, but when I register it as a function it will only work with the explicit return otherwise it will return '0' for any result (or ERROR obviously)

Is this an issue with the way you are handling the return from the code?? Does it mean I have to explicitly return something??