Upgrading to Python3.6 throws an error

We are using virtualenv for python. We tried to upgrade from Python2.7 to 3.6, and we get the below error.

We are using nodeenv and plugins like serverless-python-requirements

Serverless: Parsing Python requirements.txt
Serverless: Installing required Python packages for runtime python3.6…

Type Error ---------------------------------------------

Cannot read property ‘toString’ of null

 For debugging logs, run again after setting the "SLS_DEBUG=*" environment variable.

Stack Trace --------------------------------------------

TypeError: Cannot read property ‘toString’ of null
at BbPromise (/home/ecofit/serverless2/serverless-installer-api/node_modules/serverless-python-requirements/index.js:98:30)
at ServerlessPythonRequirements.installRequirements (/home/ecofit/serverless2/serverless-installer-api/node_modules/serverless-python-requirements/index.js:86:12)
at ServerlessPythonRequirements.packRequirements (/home/ecofit/serverless2/serverless-installer-api/node_modules/serverless-python-requirements/index.js:135:17)
From previous event:
at PluginManager.invoke (/home/ecofit/.virtualenvs/serverless2/lib/node_modules/serverless/lib/classes/PluginManager.js:242:22)
at PluginManager.spawn (/home/ecofit/.virtualenvs/serverless2/lib/node_modules/serverless/lib/classes/PluginManager.js:254:17)
at Deploy.BbPromise.bind.then.then (/home/ecofit/.virtualenvs/serverless2/lib/node_modules/serverless/lib/plugins/deploy/deploy.js:101:50)
From previous event:
at Object.before:deploy:deploy [as hook] (/home/ecofit/.virtualenvs/serverless2/lib/node_modules/serverless/lib/plugins/deploy/deploy.js:99:10)
at BbPromise.reduce (/home/ecofit/.virtualenvs/serverless2/lib/node_modules/serverless/lib/classes/PluginManager.js:242:55)
From previous event:
at PluginManager.invoke (/home/ecofit/.virtualenvs/serverless2/lib/node_modules/serverless/lib/classes/PluginManager.js:242:22)
at PluginManager.run (/home/ecofit/.virtualenvs/serverless2/lib/node_modules/serverless/lib/classes/PluginManager.js:261:17)
at variables.populateService.then (/home/ecofit/.virtualenvs/serverless2/lib/node_modules/serverless/lib/Serverless.js:99:33)
at runCallback (timers.js:781:20)
at tryOnImmediate (timers.js:743:5)
at processImmediate [as _immediateCallback] (timers.js:714:5)
From previous event:
at Serverless.run (/home/ecofit/.virtualenvs/serverless2/lib/node_modules/serverless/lib/Serverless.js:86:74)
at serverless.init.then (/home/ecofit/.virtualenvs/serverless2/lib/node_modules/serverless/bin/serverless:39:50)
at

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Your Environment Information -----------------------------
OS: linux
Node Version: 8.4.0
Serverless Version: 1.20.2

I figured it out. It was because of my default version of Python 3.5 on ubuntu.

I upgraded to python3.6 on ubuntu and then created virtualenv for python3.6.
It fixed the problem