/tellraw @p {"text":null} - Error in log

Fixed in 1.9: In 15w35e the error message Invalid json: malformed JSON at line 1 column 3 is thrown.

@unknown, that happened very likely because JSON was strict in 15w35e. Adding double quotes around text shows

An unknown error occurred while attempting to perform this command

Can confirm for MC 1.12.1.

Couldn't process command: tellraw @p {"text":null}
java.lang.UnsupportedOperationException: JsonNull
	at com.google.gson.JsonElement.getAsString(JsonElement.java:191)
	at hh$a.a(SourceFile:62)
	at hh$a.deserialize(SourceFile:41)
	at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:69)
	at rc.a(SourceFile:492)
	at rc.a(SourceFile:517)
	at hh$a.a(SourceFile:212)
	at du.a(SourceFile:44)
	at bj.a(SourceFile:92)
	at bj.a(SourceFile:70)
	at pa.c(SourceFile:850)
	at pa.a(SourceFile:837)
	at la.a(SourceFile:37)
	at la.a(SourceFile:9)
	at hv$1.run(SourceFile:13)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at h.a(SourceFile:46)
	at net.minecraft.server.MinecraftServer.D(SourceFile:604)
	at net.minecraft.server.MinecraftServer.C(SourceFile:560)
	at chd.C(SourceFile:154)
	at net.minecraft.server.MinecraftServer.run(SourceFile:464)
	at java.lang.Thread.run(Thread.java:745)

Issue has been fixed for 1.13.1 since the command updates.

1.13.1: /tellraw @p [{"text":"null"}]

@unknown,

/tellraw @p {"text":"null"}

is something completely different than

/tellraw @p {"text":null}

Nevertheless, it's no longer possible to enter

{"text":null}