Given a collection: Unable to find source-code formatter for language: javscript. Available languages are: actionscript, ada, applescript, bash, c, c#, c++, cpp, css, erlang, go, groovy, haskell, html, java, javascript, js, json, lua, none, nyan, objc, perl, php, python, r, rainbow, ruby, scala, sh, sql, swift, visualbasic, xml, yaml { _id: 1, items: [ [1, 2, 3], [4, 5, 6] ] } db.collection.aggregate([ { $project: { items: { $concatArrays: "$items" } } } ]) Result should be: Unable to find source-code formatter for language: javscript. Available languages are: actionscript, ada, applescript, bash, c, c#, c++, cpp, css, erlang, go, groovy, haskell, html, java, javascript, js, json, lua, none, nyan, objc, perl, php, python, r, rainbow, ruby, scala, sh, sql, swift, visualbasic, xml, yaml { _id: 1, items: [1, 2, 3, 4, 5, 6] } Result is: Unable to find source-code formatter for language: javscript. Available languages are: actionscript, ada, applescript, bash, c, c#, c++, cpp, css, erlang, go, groovy, haskell, html, java, javascript, js, json, lua, none, nyan, objc, perl, php, python, r, rainbow, ruby, scala, sh, sql, swift, visualbasic, xml, yaml { _id: 1, items: [ [1, 2, 3], [4, 5, 6] ] }