Detect if twig macro argument was passed or null - macros

Question

I need to know when an argument for a twig macro is defined vs when a null was passed as the value. If I use "is defined" then that accounts for both conditions, as twig seems to set all undefined arguments to null.
For example, here are two calls, the first calling the macro without the argument, and the second with a null value for the argument:
{% import 'macros.twig' as macros %}
{{ macros.method() }}
{{ macros.method(null) }}
And this would be the macro definition:
{% macro method(value) %}
{# condition to determine if value is undefined or null? #}
{% endmacro %}

Answer 1

To have a closer look into what Twig does with the definition of macro's I've added the compiled source. It as you say, twig sets all the variables default to null, so testing whether a variable was passed to a macro will be hard
twig
{% macro vars(foo, bar, foobar) %}
{% endmacro %}
{% import _self as forms %}
{{ forms.vars(null, false) }}
compiled source
// line 1
public function macro_vars($__foo__ = null, $__bar__ = null, $__foobar__ = null, ...$__varargs__)
{
$context = $this->env->mergeGlobals(array(
"foo" => $__foo__,
"bar" => $__bar__,
"foobar" => $__foobar__,
"varargs" => $__varargs__,
));
$blocks = array();
ob_start();
try {
return ('' === $tmp = ob_get_contents()) ? '' : new Twig_Markup($tmp, $this->env->getCharset());
} finally {
ob_end_clean();
}
}