Trivial; make the error message just a pinch more explicit in case we
trip this by accident in the future.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 scripts/qapi/introspect.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
index 2b90a52f016..c72beeeed27 100644
--- a/scripts/qapi/introspect.py
+++ b/scripts/qapi/introspect.py
@@ -124,7 +124,9 @@ def indent(level):
     elif isinstance(obj, bool):
         ret += 'QLIT_QBOOL(%s)' % ('true' if obj else 'false')
     else:
-        assert False                # not implemented
+        raise NotImplementedError(
+            f"type '{type(obj).__name__}' not implemented"
+        )
     if level > 0:
         ret += ','
     return ret
-- 
2.29.2