Allow yield expressions without a RHS.

src/ast.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_AST_H_
 #define V8_AST_H_
 
 #include "src/v8.h"
 
 #include "src/assembler.h"
@@ skipping 3350 matching lines @@
     Assignment* assign =
         new(zone_) Assignment(zone_, op, target, value, pos);
     assign->Init(zone_, this);
     VISIT_AND_RETURN(Assignment, assign)
   }
 
   Yield* NewYield(Expression *generator_object,
                   Expression* expression,
                   Yield::Kind yield_kind,
                   int pos) {
+    if (!expression) expression = NewUndefinedLiteral(pos);
     Yield* yield = new(zone_) Yield(
         zone_, generator_object, expression, yield_kind, pos);
     VISIT_AND_RETURN(Yield, yield)
   }
 
   Throw* NewThrow(Expression* exception, int pos) {
     Throw* t = new(zone_) Throw(zone_, exception, pos);
     VISIT_AND_RETURN(Throw, t)
   }
 
@@ skipping 42 matching lines @@
  private:
   Zone* zone_;
   Visitor visitor_;
   AstValueFactory* ast_value_factory_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_AST_H_