Fix `return None` in CodeWriter. (GH-3795)

Cython/CodeWriter.py

@@ -449,8 +449,10 @@ class StatementWriter(DeclarationWriter):
         self._visit_indented(node.body)
 
     def visit_ReturnStatNode(self, node):
-        self.startline("return ")
-        self.visit(node.value)
+        self.startline("return")
+        if node.value is not None:
+            self.put(u" ")
+            self.visit(node.value)
         self.endline()
 
     def visit_ReraiseStatNode(self, node):

Cython/Tests/TestCodeWriter.py

@@ -107,6 +107,22 @@ class TestCodeWriter(CythonTest):
     def test_attribute(self):
         self.t(u"a.x")
 
+    def test_return_none(self):
+        self.t(u"""
+                    def f(x, y, z):
+                        return
+                    cdef f(x, y, z):
+                        return
+                    def f(x, y, z):
+                        return None
+                    cdef f(x, y, z):
+                        return None
+                    def f(x, y, z):
+                        return 1234
+                    cdef f(x, y, z):
+                        return 1234
+               """)
+
 if __name__ == "__main__":
     import unittest
     unittest.main()