Call to a member function getReasonPhrase() on null

As fgm discovered in #2721363: webprofiler timeline always reports 0, no graph:

Error: Call to a member function getReasonPhrase() on null in Drupal\webprofiler\DataCollector\HttpDataCollector->collect() (line 106 of modules/contrib/devel/webprofiler/src/DataCollector/HttpDataCollector.php).
Drupal\webprofiler\DataCollector\HttpDataCollector->collect(Object, NULL, NULL) (Line: 223)
Symfony\Component\HttpKernel\Profiler\Profiler->collect(Object, Object, NULL) (Line: 128)
Symfony\Component\HttpKernel\EventListener\ProfilerListener->onKernelResponse(Object, 'kernel.response', Object)
call_user_func(Array, Object, 'kernel.response', Object) (Line: 61)
Symfony\Component\EventDispatcher\Debug\WrappedListener->__invoke(Object, 'kernel.response', Object) (Line: 111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.response', Object) (Line: 140)
Symfony\Component\EventDispatcher\Debug\TraceableEventDispatcher->dispatch('kernel.response', Object) (Line: 184)
Symfony\Component\HttpKernel\HttpKernel->filterResponse(Object, Object, 1) (Line: 166)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 64)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 98)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 77)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 43)
Drupal\webprofiler\StackMiddleware\WebprofilerMiddleware->handle(Object, 1, 1) (Line: 50)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 628)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

This happen when the Guzzle HTTP response is NULL (for example if host is unreachable)