data Item =
  Item
    { code:: String
    , thumbUrl :: Maybe T.Text
    }
  deriving (Generic, Show, Eq, Ord)

instance ToJSON Item where
    toEncoding = genericToEncoding defaultOptions
      { omitNothingFields = True }

instance Item Game where
  parseJSON = genericParseJSON defaultOptions { omitNothingFields = True}

encodePretty [ Item {code= "foo", thumbUrl = Nothing}]

$ cabal repl --build-depends aeson-pretty                                                                                                             Sat 21:12
Resolving dependencies...
Build profile: -w ghc-8.10.7 -O1
In order, the following will be built (use -v for more details):
 - aeson-pretty-0.8.8 (lib) (requires build)
 - fake-package-0 (lib) (first run)
Starting     aeson-pretty-0.8.8 (lib)
Building     aeson-pretty-0.8.8 (lib)

Failed to build aeson-pretty-0.8.8.
Build log (
/home/hasufell/.cabal/logs/ghc-8.10.7/aeson-pretty-0.8.8-7d5e0bebeaf77dbf14fbe263246433acbce057be5e13a95f8a842096920829bb.log
):
Configuring library for aeson-pretty-0.8.8..
Preprocessing library for aeson-pretty-0.8.8..
Building library for aeson-pretty-0.8.8..
[1 of 1] Compiling Data.Aeson.Encode.Pretty ( Data/Aeson/Encode/Pretty.hs, dist/build/Data/Aeson/Encode/Pretty.o, dist/build/Data/Aeson/Encode/Pretty.dyn_o )

Data/Aeson/Encode/Pretty.hs:58:1: error:
    Could not load module ‘Data.Aeson.Encode’
    It is a member of the hidden package ‘aeson-1.5.6.0’.
    Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.
    It is a member of the hidden package ‘aeson-1.5.6.0’.
    Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.
    It is a member of the hidden package ‘aeson-1.5.6.0’.
    Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.
    It is a member of the hidden package ‘aeson-1.5.6.0’.
    Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.
    It is a member of the hidden package ‘aeson-1.5.6.0’.
    Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.
    It is a member of the hidden package ‘aeson-1.5.6.0’.
    Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.
    It is a member of the hidden package ‘aeson-1.5.6.0’.
    Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.
    It is a member of the hidden package ‘aeson-1.5.6.0’.
    Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.
    It is a member of the hidden package ‘aeson-1.5.6.0’.
    Perhaps you need to add ‘aeson’ to the build-depends in your .cabal file.
    Use -v (or `:set -v` in ghci) to see a list of the files searched for.
   |
58 | import qualified Data.Aeson.Encode as Aeson
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
cabal: Failed to build aeson-pretty-0.8.8 (which is required by
fake-package-0). See the build log above for details.

encodePretty :: aeson-0.7.0.0:Data.Aeson.Types.Class.ToJSON a => a -> Data.ByteString.Lazy.Internal.ByteString

Data.Aeson.Encode.encodeToTextBuilder

encodeToTextBuilder :: Config -> Value -> Builder
encodeToTextBuilder Config{..} = toLazyText . fromValue st
  where
    st       = PState confIndent 0 condSort
    condSort = sortBy (confCompare `on` fst)

     Generic ->
      doFmt (if e < 0 || e > 7 then Exponent else Fixed)
            (is,e)

fromScientific :: Scientific -> Builder
fromScientific s = formatScientificBuilder format prec s
  where
    (format, prec)
      | base10Exponent s < 0 = (Generic, Nothing)
      | otherwise            = (Fixed,   Just 0)

"intBillion" : 1000000000

prettyFormatter :: S.Scientific -> Builder
prettyFormatter n
    | S.isFloating n == True = formatScientificBuilder S.Generic Nothing n
    | otherwise =formatScientificBuilder S.Generic (Just 0) n -- output no digits after decimal point

"double0" : 0,
"doubleHalf" : 0.5,
"intTwo" : 2,
"intMillion" : 1000000
"intBillion" : 1.0e9

    In the use of ‘Aeson.fromValue’ (imported from Data.Aeson.Encode):
    Deprecated: "Use 'encodeToTextBuilder' instead"
In-place registering aeson-pretty-0.7.1...
Preprocessing executable 'aeson-pretty' for aeson-pretty-0.7.1...
[1 of 2] Compiling Paths_aeson_pretty ( dist/dist-sandbox-75adb5f/build/autogen/Paths_aeson_pretty.hs, dist/dist-sandbox-75adb5f/build/aeson-pretty/aeson-pretty-tmp/Paths_aeson_pretty.o )
[2 of 2] Compiling Main             ( cli-tool/Main.hs, dist/dist-sandbox-75adb5f/build/aeson-pretty/aeson-pretty-tmp/Main.o )
Failed to load interface for ‘Data.Aeson.Encode.ByteString’
There are files missing in the ‘aeson-0.7.0.6’ package,