fixed invalid test

Summary: The `block` paramenter is marked as nonnull, so we can't pass `nil` directly in.

Reviewed By: dshahidehpour

Differential Revision: D4929692

fbshipit-source-id: a35ef2940d6986f4ff55444d8a99ba17eb7c677e

YogaKit/Tests/YogaKitTests.m

@@ -21,7 +21,8 @@
 - (void)testConfigureLayoutIsNoOpWithNilBlock
 {
   UIView *view = [[UIView alloc] initWithFrame:CGRectZero];
-  XCTAssertNoThrow([view configureLayoutWithBlock:nil]);
+  id block = nil;
+  XCTAssertNoThrow([view configureLayoutWithBlock:block]);
 }
 
 - (void)testConfigureLayoutBlockWorksWithValidBlock