Add missing docstring for BadTTL exception.

diff --git a/dns/ttl.py b/dns/ttl.py
index 4341c49904354d07e7ff8ac8ee19f0c64874972c..2f4d01181e8fca8760a5137b3fd2c1f77f0eccd8 100644 (file)
--- a/dns/ttl.py
+++ b/dns/ttl.py
@@ -18,7 +18,7 @@
 import dns.exception
 
 class BadTTL(dns.exception.SyntaxError):
-    pass
+    """DNS TTL value is not well-formed."""
 
 def from_text(text):
     """Convert the text form of a TTL to an integer.