Parser::Declare follow-up to r38979.

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index 945af996676b88a3ca3492e12b6296d009800760..3ae53f7682d2d19827fc683d70cdee9d7a8605d0 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -1688,6 +1688,7 @@ Variable* Parser::Declare(Declaration* declaration,
     } else {
       ReportMessage(MessageTemplate::kParamDupe);
     }
+    return nullptr;
   }
   if (sloppy_mode_block_scope_function_redefinition) {
     ++use_counts_[v8::Isolate::kSloppyModeBlockScopedFunctionRedefinition];