db.runCommand({aggregate:"collName", pipeline: [{$project: {firstMove : "$iDontExist"}},{$group:{_id:"$firstMove"}}]})

Tue Nov 29 09:56:54 [conn1]  chess Assertion failure pValue->getType() != Undefined db/pipeline/document.cpp 104
0x88d327 0x9091a7 0x911770 0x9f0126 0x9f550b 0x9f53ac 0x9f3e59 0x9e50af 0xca0ca7 0xc7a5eb 0xc7b128 0xc7b617 0xc5c44e 0xc5d88f 0xbde271 0xbdeef6 0xd1b601 0x9abe9d 0x7fe4a0ac9d8c 0x7fe49f7d604d 
 ./mongod(_ZN5mongo15printStackTraceERSo+0x27) [0x88d327]
 ./mongod(_ZN5mongo12sayDbContextEPKc+0x5e) [0x9091a7]
 ./mongod(_ZN5mongo8assertedEPKcS1_j+0x122) [0x911770]
 ./mongod(_ZN5mongo8Document8addFieldERKSsRKN5boost13intrusive_ptrIKNS_5ValueEEE+0x4e) [0x9f0126]
 ./mongod(_ZN5mongo19DocumentSourceGroup12makeDocumentERKN5boost16unordered_detail13hash_iteratorISaISt4pairIKNS1_13intrusive_ptrIKNS_5ValueEEESt6vectorINS5_INS_11AccumulatorEEESaISC_EEEENS2_9ungroupedEEE+0x83) [0x9f550b]
 ./mongod(_ZN5mongo19DocumentSourceGroup8populateEv+0x500) [0x9f53ac]
 ./mongod(_ZN5mongo19DocumentSourceGroup3eofEv+0x27) [0x9f3e59]
 ./mongod(_ZN5mongo8Pipeline3runERNS_14BSONObjBuilderERSsN5boost13intrusive_ptrINS_14DocumentSourceEEE+0x117) [0x9e50af]
 ./mongod(_ZN5mongo15PipelineCommand3runERKSsRNS_7BSONObjEiRSsRNS_14BSONObjBuilderEb+0x699) [0xca0ca7]
 ./mongod(_ZN5mongo12_execCommandEPNS_7CommandERKSsRNS_7BSONObjEiRNS_14BSONObjBuilderEb+0x8e) [0xc7a5eb]
 ./mongod(_ZN5mongo11execCommandEPNS_7CommandERNS_6ClientEiPKcRNS_7BSONObjERNS_14BSONObjBuilderEb+0x896) [0xc7b128]
 ./mongod(_ZN5mongo12_runCommandsEPKcRNS_7BSONObjERNS_11_BufBuilderINS_16TrivialAllocatorEEERNS_14BSONObjBuilderEbi+0x358) [0xc7b617]
 ./mongod(_ZN5mongo11runCommandsEPKcRNS_7BSONObjERNS_5CurOpERNS_11_BufBuilderINS_16TrivialAllocatorEEERNS_14BSONObjBuilderEbi+0x46) [0xc5c44e]
 ./mongod(_ZN5mongo8runQueryERNS_7MessageERNS_12QueryMessageERNS_5CurOpES1_+0x223) [0xc5d88f]
 ./mongod() [0xbde271]
 ./mongod(_ZN5mongo16assembleResponseERNS_7MessageERNS_10DbResponseERKNS_11HostAndPortE+0x33f) [0xbdeef6]
 ./mongod(_ZN5mongo16MyMessageHandler7processERNS_7MessageEPNS_21AbstractMessagingPortEPNS_9LastErrorE+0xe1) [0xd1b601]
 ./mongod(_ZN5mongo3pms9threadRunEPNS_13MessagingPortE+0x351) [0x9abe9d]
 /lib/x86_64-linux-gnu/libpthread.so.0(+0x6d8c) [0x7fe4a0ac9d8c]
 /lib/x86_64-linux-gnu/libc.so.6(clone+0x6d) [0x7fe49f7d604d]
Tue Nov 29 09:56:54 [conn1] 

***aborting after assert() failure in a debug/test build


Tue Nov 29 09:56:54 Got signal: 6 (Aborted).