MetricsPortal query API throws an uninformative 500 if you POST without Content-type: application/json

[orborde]

$ curl http://[redacted]:8080/api/v1/datapoints/query --header 'Host: [redacted]' -vvv  -d'{
   "start_absolute":1581292800000,
   "end_absolute":1581379200000,
   "metrics":[
     {
       "name":"redacted/metric_name",

     }
   ]
 }'
*   Trying [redacted]...
* Connected to [redacted] ([redacted]) port 8080 (#0)
> POST /api/v1/datapoints/query HTTP/1.1
> Host: [redacted]
> User-Agent: curl/7.47.0
> Accept: */*
> Content-Length: 139
> Content-Type: application/x-www-form-urlencoded
> 
* upload completely sent off: 139 out of 139 bytes
< HTTP/1.1 500 Internal Server Error
< Date: Tue, 25 Feb 2020 21:08:34 GMT
< Content-Length: 0
< 
* Connection #0 to host [redacted] left intact

There's a stack in the MetricsPortal log:

  "exception": {
    "type": "java.lang.NullPointerException",
    "message": null,
    "backtrace": [
      "at com.fasterxml.jackson.databind.ObjectMapper.treeToValue(ObjectMapper.java:2746)",
      "at controllers.KairosDbProxyController.queryMetrics(KairosDbProxyController.java:155)",
      "at portal.Routes$$anonfun$routes$1$$anonfun$applyOrElse$27$$anonfun$apply$27.apply(Routes.scala:767)",
      "at portal.Routes$$anonfun$routes$1$$anonfun$applyOrElse$27$$anonfun$apply$27.apply(Routes.scala:767)",
      "at play.core.routing.HandlerInvokerFactory$$anon$4.resultCall(HandlerInvoker.scala:146)",
      "at play.core.routing.HandlerInvokerFactory$JavaActionInvokerFactory$$anon$8$$anon$2$$anon$1.invocation(HandlerInvoker.scala:115)",
      "at play.core.j.JavaAction$$anon$1.call(JavaAction.scala:111)",
      "at com.arpnetworking.play.metrics.MetricsActionWrapper.call(MetricsActionWrapper.java:60)",
      "at play.core.j.JavaAction$$anonfun$9.apply(JavaAction.scala:170)",
      "at play.core.j.JavaAction$$anonfun$9.apply(JavaAction.scala:170)",
      "at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24)",
      "at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)",
      "at play.core.j.HttpExecutionContext$$anon$2.run(HttpExecutionContext.scala:64)",
      "at play.api.libs.streams.Execution$trampoline$.execute(Execution.scala:71)",
      "at play.core.j.HttpExecutionContext.execute(HttpExecutionContext.scala:56)",
      "at scala.concurrent.impl.Future$.apply(Future.scala:31)",
      "at scala.concurrent.Future$.apply(Future.scala:494)",
      "at play.core.j.JavaAction.apply(JavaAction.scala:170)",
      "at play.api.mvc.Action$$anonfun$apply$2.apply(Action.scala:97)",
      "at play.api.mvc.Action$$anonfun$apply$2.apply(Action.scala:90)",
      "at scala.concurrent.Future$$anonfun$flatMap$1.apply(Future.scala:253)",
      "at scala.concurrent.Future$$anonfun$flatMap$1.apply(Future.scala:251)",
      "at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:36)",
      "at akka.dispatch.BatchingExecutor$AbstractBatch.processBatch(BatchingExecutor.scala:55)",
      "at akka.dispatch.BatchingExecutor$BlockableBatch$$anonfun$run$1.apply$mcV$sp(BatchingExecutor.scala:91)",
      "at akka.dispatch.BatchingExecutor$BlockableBatch$$anonfun$run$1.apply(BatchingExecutor.scala:91)",
      "at akka.dispatch.BatchingExecutor$BlockableBatch$$anonfun$run$1.apply(BatchingExecutor.scala:91)",
      "at scala.concurrent.BlockContext$.withBlockContext(BlockContext.scala:72)",
      "at akka.dispatch.BatchingExecutor$BlockableBatch.run(BatchingExecutor.scala:90)",
      "at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:40)",
      "at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(ForkJoinExecutorConfigurator.scala:44)",
      "at akka.dispatch.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)",
      "at akka.dispatch.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)",
      "at akka.dispatch.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)",
      "at akka.dispatch.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)"
    ],

If you add --header 'Content-type: application/json', the above curl invocation works.

The expected behavior here is either:
(A) MetricsPortal parses the JSON even if the Content-type header is not present, or
(B) Returns a 400 Bad Request with an error page requesting the Content-type header to be set.