How to correctly use ly:warning-located?

[Simon Albrecht]

Hello,

the doc string for ly:warning-located says

‘Function: ly:warning-located location str rest
A Scheme callable function to issue the warning str at the specified 
location in an input file. The message is formatted with format and rest.’

However, with this example

%%%%%%%%%%%
\version "2.19.36"

m =
#(define-music-function ()()
   (ly:warning-located *location* "Here, \\m should be replaced with 
\\melisma.")
   #{ \melisma #})

<<
  {
    c'1\m d\melismaEnd
  }
  \addlyrics { test test }
>>
%%%%%%%%

I get

document.ly:5:4: Wrong type argument in position 1 (expecting string): 
#<procedure *location* ()>

What is the correct way?

TIA, Simon