allow negative duration via internal API (#3573)

src/Validator/Constraints/TimesheetBasicValidator.php

@@ -132,9 +132,6 @@ final class TimesheetBasicValidator extends ConstraintValidator
                 ->addViolation();
         }
 
-        $pathStart = 'begin';
-        $pathEnd = 'end';
-
         $projectBegin = $project->getStart();
         $projectEnd = $project->getEnd();
 
@@ -142,10 +139,13 @@ final class TimesheetBasicValidator extends ConstraintValidator
             return;
         }
 
+        $pathStart = 'begin';
+        $pathEnd = 'end';
+
         $timesheetStart = $timesheet->getBegin();
         $timesheetEnd = $timesheet->getEnd();
 
-        if (null !== $timesheetStart && $pathStart !== null) {
+        if (null !== $timesheetStart) {
             if (null !== $projectBegin && $timesheetStart->getTimestamp() < $projectBegin->getTimestamp()) {
                 $context->buildViolation('The project has not started at that time.')
                     ->atPath($pathStart)
@@ -161,7 +161,7 @@ final class TimesheetBasicValidator extends ConstraintValidator
             }
         }
 
-        if (null !== $timesheetEnd && $pathEnd !== null) {
+        if (null !== $timesheetEnd) {
             if (null !== $projectEnd && $timesheetEnd->getTimestamp() > $projectEnd->getTimestamp()) {
                 $context->buildViolation('The project is finished at that time.')
                     ->atPath($pathEnd)