[Sequence of command cause Null check exception]

[bnjun96]

Before creating a feature request make sure the suggestion fit within our principles

Unhandled exception:
type 'Null' is not a subtype of type 'String' in type cast

#0      new FvmConfig.fromMap (package:fvm/src/models/config_model.dart:41)
#1      new FvmConfig.fromJson (package:fvm/src/models/config_model.dart:31)
#2      ConfigService.read (package:fvm/src/services/config_service.dart:21)
<asynchronous suspension>
#3      ProjectService.getByDirectory (package:fvm/src/services/project_service.dart:18)
<asynchronous suspension>
#4      useVersionWorkflow (package:fvm/src/workflows/use_version.workflow.dart:15)
<asynchronous suspension>
#5      UseCommand.run (package:fvm/src/commands/use_command.dart:86)
<asynchronous suspension>
#6      CommandRunner.runCommand (package:args/command_runner.dart:209)
<asynchronous suspension>
#7      FvmCommandRunner.run (package:fvm/src/runner.dart:72)
<asynchronous suspension>
#8      main (file:///private/tmp/fvm-20211027-54069-11mnwzs/fvm-2.2.3/bin/main.dart:6)
<asynchronous suspension>

Steps to procedure

1. run fvm use 2.2.0 --flavor dev
2. run fvm use 1.22.6 --flavor prod

Hope to enhance feature, pre set fvm_config flutterSdkVersion with version.
Example run fvm use 2.2.0 --flavor dev
fvm_config.json will be

{
"flutterSdkVersion": null 1.22.6,
"flavors": {
"dev": "1.22.6"
}
}

Else throw to developer run fvm use first before with flavor.