validation - silex validator using last constraint from previous collection item -

based on tutorial validation in silex i've created constraint:

    $constraint = new assert\collection([         'token' => [             new assert\notblank(),             new assert\length(['min' => constant::token_length, 'max' => constant::token_length]),         ],         'languagecode' => [             new assert\notblank(),             new assert\choice(['choices' => [constant::language_code_de, constant::language_code_en]])         ],         'startdate' => [             new assert\notblank(),             new assert\date()         ],         'enddate' => [             new assert\notblank(),             new assert\date()         ],         'duration' => [             new assert\greaterthanorequal(['value' => 1])         ],     ]); 

which should match following structures (here json):

{     "token": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",     "languagecode": "de",     "startdate": "2016-01-01",     "enddate": "2016-01-05",     "duration": 1 } 

and

{     "token": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",     "languagecode": "de",     "startdate": "2016-01-01",     "enddate": "2016-01-05" } 

while first example validated expected, second (with optional duration) respond in strange behavior: constraints "enddate" used:

object(symfony\component\validator\constraintviolationlist)[154]   private 'violations' =>      array (size=1)       0 =>          object(symfony\component\validator\constraintviolation)[158]           private 'message' => string 'this field missing.' (length=22)           private 'messagetemplate' => string 'this field missing.' (length=22)           private 'parameters' =>              array (size=1)               '{{ field }}' => string '"duration"' (length=10)           private 'plural' => null           private 'root' =>              array (size=4)               'token' => string 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855' (length=64)               'languagecode' => string 'de' (length=2)               'startdate' => string '2016-01-01' (length=10)               'enddate' => string '2016-01-05' (length=10)           private 'propertypath' => string '[duration]' (length=10)           private 'invalidvalue' => null           private 'constraint' =>              object(symfony\component\validator\constraints\date)[136]               public 'message' => string 'this value not valid date.' (length=31)               public 'payload' => null               public 'groups' =>                  array (size=1)                   0 => string 'default' (length=7)           private 'code' => string '2fa2158c-2a7f-484b-98aa-975522539ff8' (length=36)           private 'cause' => null 

i don't see reason that....

try add parameter allowmissingfields

$constraint = new assert\collection([     'allowmissingfields' => true,     'fields' => [asserts...] ]);