Updating yield.

hy/compiler.py

@@ -453,11 +453,14 @@ class HyASTCompiler(object):
         return ast.Pass(lineno=expr.start_line, col_offset=expr.start_column)
 
     @builds("yield")
-    @checkargs(1)
+    @checkargs(max=1)
     def compile_yield_expression(self, expr):
         expr.pop(0)
+        value = None
+        if expr != []:
+            value = self.compile(expr.pop(0))
         return ast.Yield(
-            value=self.compile(expr.pop(0)),
+            value=value,
             lineno=expr.start_line,
             col_offset=expr.start_column)
 

tests/compilers/test_ast.py

@@ -210,7 +210,6 @@ def test_ast_good_yield():
 
 def test_ast_bad_yield():
     "Make sure AST can't compile invalid yield"
-    cant_compile("(yield)")
     cant_compile("(yield 1 2)")