upip: Workaround _os.getenv() accepting only 1 argument.

upip/metadata.txt

@@ -1,6 +1,6 @@
 srctype = micropython-lib
 type = module
-version = 0.6
+version = 0.6.1
 author = Paul Sokolovsky
 extra_modules = upip_errno, upip_gzip, upip_utarfile
 desc = Simple package manager for MicroPython.

upip/setup.py

@@ -6,7 +6,7 @@ from setuptools import setup
 
 
 setup(name='micropython-upip',
-      version='0.6',
+      version='0.6.1',
       description='Simple package manager for MicroPython.',
       long_description='Simple package manager for MicroPython, targetting to be self-hosted (but not yet there). Compatible only with packages without custom setup.py code.',
       url='https://github.com/micropython/micropython/issues/405',

upip/upip.py

@@ -249,7 +249,7 @@ def main():
             fatal("Unknown/unsupported option: " + opt)
 
     if install_path is None:
-        install_path = os.getenv("MICROPYPATH", DEFAULT_MICROPYPATH)
+        install_path = os.getenv("MICROPYPATH") or DEFAULT_MICROPYPATH
 
     install_path = install_path.split(":", 1)[0]