sample code in javadoc of Map#spreadMap() don't works

At the GDK document of Map#toSpreadMap(),

http://groovy.codehaus.org/groovy-jdk/java/util/Map.html#toSpreadMap()

says:

For examples, if there is defined a function like as

def fn(a, b, c, d)

Unknown macro: { return a + b + c + d }

, then all of the following three have the same meaning.
println fn(a:1, [b:2, c:3].toSpreadMap(), d:4)
println fn(a:1, *:[b:2, c:3], d:4)
println fn(a:1, b:2, c:3, d:4)

I think there are at least 2 problems here.

1) fn should take Map parameter like:

def fn(Map m) { return m.a + m.b + m.c + m.d }

2) I changed it in 1) way but I get following error at the line calling toSpreadMap().

Caught: groovy.lang.MissingMethodException: No signature of method: d.fn() is applicable for argument types: (java.util.LinkedHashMap, groovy.lang.SpreadMap) values: [[a:1, d:4], [:]]
Possible solutions: fn(java.util.Map), run(), run(), any(), run(java.io.File, [Ljava.lang.String, any(groovy.lang.Closure)
at d.run(d.groovy:3)