Creating new brick with mason new <NAME> with empty mason.yaml throws error.

[mtwichel]

Steps to Reproduce

1. Run mason init in new directory
2. Open generated mason.yaml and delete all the contents
3. Run mason new test

You'll receive the following stack trace:

Marcuss-MBP-2:temp mtwichel$ mason new test
Unhandled exception:
ParsedYamlException: line 1, column 1: Not a map
  ╷
1 │ 
  │ ^
  ╵
#0      checkedYamlDecode (package:checked_yaml/checked_yaml.dart:43:5)
#1      NewCommand.run (package:mason/src/commands/new_command.dart:68:23)
#2      CommandRunner.runCommand (package:args/command_runner.dart:197:27)
#3      CommandRunner.run.<anonymous closure> (package:args/command_runner.dart:112:25)
#4      new Future.sync (dart:async/future.dart:223:31)
#5      CommandRunner.run (package:args/command_runner.dart:112:14)
#6      main (file:///Users/mtwichel/.pub-cache/hosted/pub.dartlang.org/mason-0.0.1-dev.15/bin/mason.dart:27:20)
#7      _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:299:32)
#8      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)

Expected Behavior

I would expect the CLI to generate a new bricks: entry in mason.yaml, then add my new brick to the file.

Background

I stumbled across this as I was trying out the new commands. The first thing I tried was mason init, said "cool this is great, I'll try it with my own template", then deleted everything that had generated from mason.yaml and tried mason new.

I believe this is occurring because the yaml parser isn't finding a valid yaml schema in the file because it's completely empty.

Potential Solutions

Two ideas I have:

• Add try/catch to reading in mason.yaml and if something goes wrong, provide a more friendly message
• Before parsing yaml file, make sure the file isn't empty. If it is, either show an error message or add bricks: entry

Let me know if you approve of these solution(s). I'm happy to submit a PR if need be.