The bug

Expected command exceptions (com.mojang.brigadier.exceptions.CommandSyntaxException) are written to the log file, for example when a selector cannot find an entity or when the syntax of a command is wrong. This can cause huge log files (for example 5 GB, see image-2017-11-12-21-12-13-730.png) when commands are running every tick.
Especially with the command changes most of the previously used commands are now incorrect and cause syntax errors.

These expected exceptions should be normal command feedback and therefore nothing should be logged.

Note: Exceptions happening because a command malfunctions should probably be logged.

Affected situations

• functions was fixed
• Commands run in chat (including using written books)

  /give @s minecraft:written_book{author:"a",title:"a",pages:["{\"\":\"click\",\"clickEvent\":{\"action\":\"run_command\",\"value\":\"/kill @e[type=item]\"}}"]}
  

• Commands run by command blocks (including minecart command blocks)

  /give @s minecraft:written_book{author:"a",title:"a",pages:["{\"\":\"click\",\"clickEvent\":{\"action\":\"run_command\",\"value\":\"/kill @e[type=item]\"}}"]}
  

• Command run when clicking signs

  /setblock ~ ~ ~ sign{Text1:"{\"text\":\"click\",\"clickEvent\":{\"action\":\"run_command\",\"value\":\"/kill @e[type=item]\"}}"}