When running `arc diff` or `arc patch` commands, arcanist makes an API call to `conduit.querydiffs`. This API method returns an error, which causes arcanist to throw an exception. The error is: `Array for %Ld conversion is empty. Query: id IN (%Ld)`.
Here is output from arcanist with the `--trace` flag:
```
>>> [23] <conduit> differential.querydiffs() <bytes = 196>
>>> [24] <http> /api/differential.querydiffs
<<< [24] <http> 151,358 us
<<< [23] <conduit> 151,692 us
[2017-01-10 21:22:55] EXCEPTION: (ConduitClientException) ERR-CONDUIT-CORE: Array for %Ld conversion is empty. Query: id IN (%Ld) at [<phutil>/src/conduit/ConduitFuture.php:58]
arcanist(head=stable, ref.master=ade25facfdf2, ref.stable=9503b941cc02), drupal(), phutil(head=stable, ref.master=c5848b71c10f, ref.stable=35b57f7ab524)
#0 ConduitFuture::didReceiveResult(array) called at [<phutil>/src/future/FutureProxy.php:58]
#1 FutureProxy::getResult() called at [<phutil>/src/future/FutureProxy.php:35]
#2 FutureProxy::resolve() called at [<phutil>/src/conduit/ConduitClient.php:64]
#3 ConduitClient::callMethodSynchronous(string, array) called at [<arcanist>/src/workflow/ArcanistDiffWorkflow.php:2246]
#4 ArcanistDiffWorkflow::loadActiveLocalCommitInfo() called at [<arcanist>/src/workflow/ArcanistDiffWorkflow.php:2144]
#5 ArcanistDiffWorkflow::getGitUpdateMessage() called at [<arcanist>/src/workflow/ArcanistDiffWorkflow.php:2110]
#6 ArcanistDiffWorkflow::getDefaultUpdateMessage() called at [<arcanist>/src/workflow/ArcanistDiffWorkflow.php:1887]
#7 ArcanistDiffWorkflow::getUpdateMessage(array, NULL) called at [<arcanist>/src/workflow/ArcanistDiffWorkflow.php:773]
#8 ArcanistDiffWorkflow::buildRevisionFromCommitMessage(ArcanistDifferentialCommitMessage) called at [<arcanist>/src/workflow/ArcanistDiffWorkflow.php:478]
#9 ArcanistDiffWorkflow::run() called at [<arcanist>/scripts/arcanist.php:394]
```
I've been able to reproduce this in the Conduit web interface:
{F2333994}
If I enter values for both arguments (ids and revisionIDs), the error does not occur. However, normal usage of arcanist is broken because arcanist only provides revision IDs to the `conduit.querydiffs` method.
### Phabricator version information:
```
phabricator 7ea1bd5a5a44361ebec617b0ae17e1fac965f711 (Mon, Jan 9)
arcanist ade25facfdf22aed1c1e20fed3e58e60c0be3c2b (Thu, Jan 5)
phutil c5848b71c10fb585b2cfdfaaee13aec2ba163c8d (Thu, Jan 5)
```
### Arcanist version information
also tested with previous versions dating back to October 2016.
```
$ arc version
arcanist 9503b941cc02be637d967bb50cfb25f852e071e4 (7 Jan 2017)
libphutil 35b57f7ab52454f697681f034bbad978658a2ff4 (7 Jan 2017)
```