?$format=json does not work when entity or collection is nonexistent

ArtSalesOrder/0.0.1-SNAPSHOT/CustomerNonExixtent?$format=json

Regarding the above query the Entity ‘CustomerNonExixtent’ does not exist . But while returning the response it is arriving in xml format even though we request json format. On debugging we found that the uriInfo object creation results in an exception during queries like this, hence the ContentNegotiator switches to the default xml format. Is this behavior expected ?