[LibTooling] Fix build breakage from commit 7b7ce6683ee.

On configurations with -Werror,-Wmissing-field-initializers, the commit does not compile. This commit fixes the offending line.

Original Differential Revision: https://reviews.llvm.org/D60408

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@358705 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Tooling/Refactoring/Transformer.cpp b/lib/Tooling/Refactoring/Transformer.cpp
index 3a7a3ff..57f6659 100644
--- a/lib/Tooling/Refactoring/Transformer.cpp
+++ b/lib/Tooling/Refactoring/Transformer.cpp
@@ -172,7 +172,8 @@
                               SmallVector<ASTEdit, 1> Edits) {
   M.setAllowBind(true);
   // `tryBind` is guaranteed to succeed, because `AllowBind` was set to true.
-  return RewriteRule{*M.tryBind(RewriteRule::RootId), std::move(Edits)};
+  return RewriteRule{*M.tryBind(RewriteRule::RootId), std::move(Edits),
+                     nullptr};
 }
 
 constexpr llvm::StringLiteral RewriteRule::RootId;