Fix newline handling after yield

YieldExpressions can only be defined as:
 * `yield`
 * `yield` [no nlb] AssignmentExpression
 * `yield` [no nlb] `*` AssignmentExpression

lib/parse.js

@@ -1174,17 +1174,23 @@ function parse($TEXT, options) {
         var has_expression = true;
         var tmp;
 
-        // Get expression behind yield, default to value `undefined` stored as `null` in ast
-        // Expression must start on same line, yield* has a mandatory expression
-        if (is("operator", "*")) {
-            star = true;
-            next();
-            if (S.token.nlb) {
-                unexpected(S.prev);
-            }
-        } else if (can_insert_semicolon() ||
+        // Attempt to get expression or star (and then the mandatory expression)
+        // behind yield on the same line.
+        //
+        // If nothing follows on the same line of the yieldExpression,
+        // it should default to the value `undefined` for yield to return.
+        // In that case, the `undefined` stored as `null` in ast.
+        //
+        // Note 1: It isn't allowed for yield* to close without an expression
+        // Note 2: If there is a nlb between yield and star, it is interpret as
+        //         yield <explicit undefined> <inserted automatic semicolon> *
+        if (can_insert_semicolon() ||
             (is("punc") && PUNC_AFTER_EXPRESSION(S.token.value))) {
             has_expression = false;
+
+        } else if (is("operator", "*")) {
+            star = true;
+            next();
         }
 
         return new AST_Yield({