Codegen Android: handle nullable getConstants() properties generation.

Summary:
The GenerateModuleJavaSpec.js mistakenly treated nullable getConstants() properties as required, such that the Java spec will throw an exception when the properties are missing. This fixed it.

Note that the JavaPoet-based generator got this correct already.

Changelog: [Internal]

Differential Revision: D24381941

fbshipit-source-id: c95d2181c66443e2191318f09b6454a5296009e4

packages/react-native-codegen/src/generators/modules/GenerateModuleJavaSpec.js

@@ -203,8 +203,7 @@ function buildGetConstantsMethod(
     const rawProperties =
       methodTypeAnnotation.returnTypeAnnotation.properties || [];
     rawProperties.forEach(p => {
-      // TODO(T76712813): Should we push to optionalProps if the constant is nullable?
-      if (p.optional) {
+      if (p.optional || p.typeAnnotation.type === 'NullableTypeAnnotation') {
         optionalProps.push(p.name);
       } else {
         requiredProps.push(p.name);