ifneq inside a function

[Ken Smith]

I can't justify to myself why this makefile

define something
  ifneq (,)
    $(warning weird)
  endif
endef

$(call something)

generates the following output

testcase.mk:6: weird
testcase.mk:6: *** missing separator.  Stop.

What I'm trying to do is rudimentary checking of the parameters passed
to a function.  I know that the function I am writing should take two
parameters so I'm checking to see if $(3) is empty or nonempty.  If it
is nonempty, I want to end processing with $(error).  What is the idiomatic
way of doing this?
-- 
Ken Smith