PHP filtering - detecting filter failures - php

Question

Update: It appears I had snipped out the wrong parts when whittling this down to a short/concise example.
I appears to (incorrectly!!) used if(empty(0)) to detect validation failure when using filter_var_array and FILTER_VALIDATE_INT.
How would be best to do so?
http://codepad.viper-7.com/Z8MLLj
$positiveIntegerFilter = array('filter' => FILTER_VALIDATE_INT,
'options' => array(
'min_range' => 0
)
);
$filter = array(
'apples' => $positiveIntegerFilter,
'oranges' => $positiveIntegerFilter,
'pears' => $positiveIntegerFilter,
'bananas' => $positiveIntegerFilter,
'tangerine' => $positiveIntegerFilter
);
$values = Array(
"apples" => 2,
"oranges" => 4,
"pears" => 0,
"bananas" => -2,
"grapefruit" => 1
);
//Apply filter, and return only what validates
$filteredValues = filter_var_array( $values, $filter );
echo "values: ";
print_r($values);
echo "<br/>";
echo "filteredValues: ";
print_r($filteredValues);
echo "<br/>";
echo "<br/>";
//Examine filtered array for missing parts
foreach($filter as $key => $value) {
echo "key = " . $key . " // value = " . $filteredValues[$key] . "(" . (gettype($filteredValues[$key])) .")". "<br/>" . PHP_EOL;
if(empty($filteredValues[$key])) { //should test if(!isset()) ?
throw new \InvalidArgumentException("Invalid information object on key: `" . $key . "`");
}
}