The bug
When placing a sign (with either /fill or /setblock) with any NBT without explicitly setting `Text1`, `Text2`, `Text3` and `Text4`, shows the message "An unexpected error occurred trying to execute that command", eventhough the sign seems to be placed correctly. This leads to the block nbt not being able to be used in things like /data modify.
How to reproduce
# the following commands work:
setblock ~ ~ ~ minecraft:spruce_sign
setblock ~ ~ ~ minecraft:spruce_sign{Text1:"\"\"",Text2:"\"\"",Text3:"\"\"",Text4:"\"\""}
# the following commands don't work:
setblock ~ ~ ~ minecraft:spruce_sign{Text1:"\"\""}
setblock ~ ~ ~ minecraft:spruce_sign{Color:"blue"}
# trying to copy Text1 to an entity's name doesn't work if it throws the error message:
summon minecraft:armor_stand ~ ~ ~ {CustomNameVisible:1b,Tags:["this"]}
setblock ~ ~ ~ minecraft:spruce_sign{Text1:"{\"score\":{\"objective\":\"tmp\",\"name\":\"@e[limit=1,tag=this]\"}}"}
data modify entity @e[tag=this,limit=1] CustomName set from block ~ ~ ~ Text1
# --> the name doesn't update
The bug is not explicitly setting all the 4 Text tags raises a NPE.