Fabric: Fixed bug in node management in FabricUIManager
Fabric: Fixed bug in node management in FabricUIManager

Summary: Suddenly, `{}` means `{nullptr}`, not `empty list`.

Reviewed By: mdvacca

Differential Revision: D7376347

fbshipit-source-id: 76f81eebe046ae592f0a42be7bcaa0587732c2a9

arthuralee/react-native,hoangpham95/react-native,hammerandchisel/react-native,janicduplessis/react-native,hammerandchisel/react-native,hoangpham95/react-native,facebook/react-native,hammerandchisel/react-native,facebook/react-native,javache/react-native,javache/react-native,facebook/react-native,myntra/react-native,myntra/react-native,javache/react-native,pandiaraj44/react-native,myntra/react-native,javache/react-native,facebook/react-native,exponent/react-native,janicduplessis/react-native,pandiaraj44/react-native,hoangpham95/react-native,myntra/react-native,exponent/react-native,javache/react-native,javache/react-native,janicduplessis/react-native,facebook/react-native,exponentjs/react-native,myntra/react-native,myntra/react-native,exponentjs/react-native,hoangpham95/react-native,facebook/react-native,janicduplessis/react-native,exponent/react-native,janicduplessis/react-native,arthuralee/react-native,javache/react-native,hammerandchisel/react-native,arthuralee/react-native,exponent/react-native,exponent/react-native,janicduplessis/react-native,hoangpham95/react-native,javache/react-native,exponent/react-native,exponent/react-native,exponentjs/react-native,exponentjs/react-native,hammerandchisel/react-native,hammerandchisel/react-native,pandiaraj44/react-native,exponentjs/react-native,javache/react-native,exponentjs/react-native,exponentjs/react-native,pandiaraj44/react-native,pandiaraj44/react-native,myntra/react-native,pandiaraj44/react-native,hoangpham95/react-native,facebook/react-native,facebook/react-native,myntra/react-native,janicduplessis/react-native,exponent/react-native,hammerandchisel/react-native,pandiaraj44/react-native,myntra/react-native,pandiaraj44/react-native,janicduplessis/react-native,arthuralee/react-native,exponentjs/react-native,arthuralee/react-native,hoangpham95/react-native,hammerandchisel/react-native,facebook/react-native,hoangpham95/react-native