THRIFT-5352: Fix construction of Py exceptions with no fields

Client: py

When no fields are present, we don't get the special constructor that
uses __setattr__ to avoid these checks. So the default constructor sets
message normally and triggers the anti-mutation tripwires.

1 files changed, 2 insertions, 0 deletions

diff --git a/test/DebugProtoTest.thrift b/test/DebugProtoTest.thrift
index 1ab0f6aea..5d0face4b 100644
--- a/test/DebugProtoTest.thrift
+++ b/test/DebugProtoTest.thrift
@@ -245,6 +245,8 @@ exception MutableException {
   1: string msg;
 } (python.immutable = "false")
 
+exception ExceptionWithoutFields {}
+
 service ServiceForExceptionWithAMap {
   void methodThatThrowsAnException() throws (1: ExceptionWithAMap xwamap);
 }