Passing a null DateTime to php function -

i have function in php want accept either datetime object or null. e.g.

function foo(datetime $adate){    if ($adate == null){        echo "you passed null variable";    } else {        echo "you passed date " . $adate->format('y-m-d');    } } 

trouble is, because function expects datetime object flips out when pass null , gives error:

catchable fatal error: argument 1 passed foo() must instance of datetime, null given,... 

how can pass null function , avoid error?

change this:

function foo(datetime $adate){ 

to this:

function foo($adate){ 

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but if still want make sure object passed datetime object can this:

function foo(datetime $adate = null){ 

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see here more examples of type hinting.