fix(nullfilter): Filters attributes in getFeatureVariableValueForType

[mnoman09]

Filters attributes getFeatureVariableValueForType before passing it to decisionService.getVariationForFeature So if attributes passed is null than it will handle it.

[coveralls]

Pull Request Test Coverage Report for Build 611

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.004%) to 88.976%

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Totals
Change from base Build 606:	0.004%
Covered Lines:	2381
Relevant Lines:	2676

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 611

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.004%) to 88.976%

---

Totals
Change from base Build 606:	0.004%
Covered Lines:	2381
Relevant Lines:	2676

---

💛 - Coveralls

[mikeproeng37]

Closing this as well as it is taken care of in #214