Fix project install against Python 2.7

pypa/setuptools#1136

changelog.d/setuptools-egg_info.build.rst

@@ -0,0 +1 @@
+Workaround https://github.com/pypa/setuptools/issues/1136

setup.py

@@ -19,6 +19,7 @@
 import subprocess
 
 from setuptools import setup
+from setuptools.command.egg_info import egg_info as egg_info_orig
 from setuptools.command.sdist import sdist as sdist_orig
 
 
@@ -30,6 +31,7 @@
 def main():
     return setup(
         cmdclass={
+            'egg_info': egg_info,
             'sdist': sdist,
         },
         version=project_version(),
@@ -69,6 +71,18 @@ def project_version():
     return version
 
 
+class egg_info(egg_info_orig):
+
+    def _ensure_stringlike(self, option, what, default=None):
+        val = getattr(self, option)
+        if val is None:
+            setattr(self, option, default)
+            return default
+        elif isinstance(val, (type(''), type(u''))):
+            return val
+        return egg_info_orig._ensure_stringlike(self, option, what, default)
+
+
 class sdist(sdist_orig):
     def run(self):
         # In case when user didn't eventually run `make version` ensure that