Using `/tweaks` with a dust limit returns `null` instead of empty array

[cygnet3]

Requesting tweaks for block214953 on Signet, when the block has no tweaks, gives me an empty array:

curl  'http://localhost:8000/tweaks/214953'

[]

However, when adding a dust limit (even just 1 sat), I get 'null' instead of an empty array:

curl 'http://localhost:8000/tweaks/214953?dustLimit=1'

null

For consistency, I would expect this to also return en empty array.

[setavenger]

Thanks for testing, fix is on dev now.