Fix .join needing only strs; first changelog entry

CHANGELOG.md

-This file will be populated once we hit 1.0.0
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
+and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Fixed
+
+- Exception that causes sbws to fall back to one measurement thread. We first
+  tried fixing something in this area with `88fae60bc` but neglected to
+remember that `.join()` wants only string arguments and can't handle a `None`.
+So fix that.
+
+
+[Unreleased]: https://github.com/pastly/simple-bw-scanner/v0.4.0...master

sbws/lib/circuitbuilder.py

@@ -164,7 +164,7 @@ class GapsCircuitBuilder(CircuitBuilder):
         insert_relays = self._random_sample_relays(
             num_missing, [r for r in path if r is not None])
         if insert_relays is None:
-            path = ','.join([r.nickname if r else None for r in path])
+            path = ','.join([r.nickname if r else str(None) for r in path])
             log.warning(
                 'Problem building a circuit to satisfy %s with available '
                 'relays in the network', path)