Fix an error when the license is unspecified

CHANGELOG.md

 # Change Log
 # Change Log
 
 
+## [Unreleased]
+
+### Fixed
+
+- Fixed an error when license is unspecified.
+
+
 ## [0.12.0] - 2018-10-17
 ## [0.12.0] - 2018-10-17
 
 
 ### Added
 ### Added

poetry/poetry.py

@@ -117,7 +117,7 @@ class Poetry:
         package.repository_url = local_config.get("repository")
         package.repository_url = local_config.get("repository")
         package.documentation_url = local_config.get("documentation")
         package.documentation_url = local_config.get("documentation")
         try:
         try:
-            license_ = license_by_id(local_config.get("license"))
+            license_ = license_by_id(local_config.get("license", ""))
         except ValueError:
         except ValueError:
             license_ = None
             license_ = None