Milestone list request returns 500 instead of 400 when productCode is missing

[ElizavetaP]

GET /api/milestones returns 500 Internal Server Error when productCode is missing.

But it should return 400 Bad Request.

[ElizavetaP]

Failed tests

[ERROR]   MilestoneControllerTests.shouldReturn400WhenProductCodeMissing:42 [HTTP status code] 
expected: 400                                                                                                                                                                
 but was: 500   

FAIL_TO_PASS: MilestoneControllerTests