TypeError: Cannot read property 'name' of undefined in rxjsFinnishRule

[zbream]

Hey, I'm liking the package!

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However, I've tried out the rules in a couple of projects, and I've consistently run into the following error during linting:

The 'rxjs-finnish' rule threw an error in 'M:/Git/_public/rxjs-finnish-rule-issue/file.ts':
TypeError: Cannot read property 'name' of undefined
    at Walker.validateNode (M:\Git\_public\rxjs-finnish-rule-issue\node_modules\rxjs-tslint-rules\dist\rules\rxjsFinnishRule.js:169:49)
    at Walker.visitPropertyDeclaration (M:\Git\_public\rxjs-finnish-rule-issue\node_modules\rxjs-tslint-rules\dist\rules\rxjsFinnishRule.js:130:18)
    at Walker.SyntaxWalker.visitNode (M:\Git\_public\rxjs-finnish-rule-issue\node_modules\tslint\lib\language\walker\syntaxWalker.js:467:22)
    at M:\Git\_public\rxjs-finnish-rule-issue\node_modules\tslint\lib\language\walker\syntaxWalker.js:535:63
    at visitNodes (M:\Git\_public\rxjs-finnish-rule-issue\node_modules\typescript\lib\typescript.js:14006:30)
    at Object.forEachChild (M:\Git\_public\rxjs-finnish-rule-issue\node_modules\typescript\lib\typescript.js:14293:21)
    at Walker.SyntaxWalker.walkChildren (M:\Git\_public\rxjs-finnish-rule-issue\node_modules\tslint\lib\language\walker\syntaxWalker.js:535:12)
    at Walker.SyntaxWalker.visitClassDeclaration (M:\Git\_public\rxjs-finnish-rule-issue\node_modules\tslint\lib\language\walker\syntaxWalker.js:63:14)
    at Walker.SyntaxWalker.visitNode (M:\Git\_public\rxjs-finnish-rule-issue\node_modules\tslint\lib\language\walker\syntaxWalker.js:314:22)
    at M:\Git\_public\rxjs-finnish-rule-issue\node_modules\tslint\lib\language\walker\syntaxWalker.js:535:63

I've narrowed it down to being caused by the declaration of an optional property (which I use extensively with strictNullChecks enabled):

myOptionalProperty?: Subject<number> = new Subject<number>();

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I've set up a minimal test repo for evaluation:

https://github.com/zbream/rxjs-finnish-rule-issue

typescript@2.8.3
tslint@5.10.0
rxjs-tslint-rules@4.3.0

You'll notice that if you comment out myOptionalProperty, everything works as expected. Also, no no-unused-variable in this project.