dmahapatro

Map.metaClass.merge = { Map rhs ->
    def lhs = delegate // or delegate.clone() to make delegate immutable
    rhs.each { k, v -> lhs[k] = lhs[k] in Map ? lhs[k].merge(v) : (lhs[k] != null ? lhs[k] && v : v) }   
    lhs
}

def a = [ foo: [ foo: true, bar: true ] ]
def b = [ foo: [ bar: false, baz: true ] ]

assert a.merge(b) == [ foo: [ foo: true, bar: false, baz: true ] ]