Riding Mobs with incorrect Ids throw a "unknown Errror" instead of telling the excecutor

When using the command "/summon Cow ~ ~ ~ {Riding:{id:Cow,Riding:{id:Cow,Riding:id:Cow}}}" it works fine, however, using the command "/summon Cow ~ ~ ~ {Riding:{id:cow,Riding:{id:Cow,Riding:id:Cow}}}" it says

An unknown error occured while attempting to perform this command

and spawns two Cows. Launcher states this:

Client> java.lang.NullPointerException
Client> at br.b(SourceFile:88) ~[13w41b.jar:?]
Client> at y.a(SourceFile:58) [13w41b.jar:?]
Client> at mp.d(SourceFile:486) [13w41b.jar:?]
Client> at mp.a(SourceFile:473) [13w41b.jar:?]
Client> at ic.a(SourceFile:37) [13w41b.jar:?]
Client> at ic.a(SourceFile:9) [13w41b.jar:?]
Client> at ek.a(SourceFile:146) [13w41b.jar:?]
Client> at ml.c(SourceFile:134) [13w41b.jar:?]
Client> at net.minecraft.server.MinecraftServer.u(SourceFile:529) [13w41b.jar:?]
Client> at net.minecraft.server.MinecraftServer.t(SourceFile:441) [13w41b.jar:?]
Client> at brh.t(SourceFile:117) [13w41b.jar:?]
Client> at net.minecraft.server.MinecraftServer.run(SourceFile:358) [13w41b.jar:?]
Client> at kt.run(SourceFile:617) [13w41b.jar:?]
Client> [18:32:18] [Client thread/INFO]: [CHAT] An unknown error occurred while attempting to perform this command

While the second command got "cow" instead of "Cow",it doesn't say that in Chat/Prev. Output , like it does with "unbalanced brackets".