Getting cryptic error if the file to return ENV object return null or {} instead

I have solved the issue myself but I thought it can be better.

It is good that it throws an error about it but the cryptic error message like this is not helping
```
remote: Module build failed: TypeError: /tmp/build_43fb00b7ca544651b6eb4730c0d0ad94/components/BuildTeam.js: Cannot convert undefined or null to object
remote: at PluginPass.UnaryExpression (/tmp/build_43fb00b7ca544651b6eb4730c0d0ad94/node_modules/babel-plugin-transform-define/lib/index.js:34:27)
remote: at newFn (/tmp/build_43fb00b7ca544651b6eb4730c0d0ad94/node_modules/babel-traverse/lib/visitors.js:276:21)
remote: at NodePath._call (/tmp/build_43fb00b7ca544651b6eb4730c0d0ad94/node_modules/babel-traverse/lib/path/context.js:76:18)
remote: at NodePath.call (/tmp/build_43fb00b7ca544651b6eb4730c0d0ad94/node_modules/babel-traverse/lib/path/context.js:48:17)
remote: at NodePath.visit (/tmp/build_43fb00b7ca544651b6eb4730c0d0ad94/node_modules/babel-traverse/lib/path/context.js:105:12)
remote: at TraversalContext.visitQueue (/tmp/build_43fb00b7ca544651b6eb4730c0d0ad94/node_modules/babel-traverse/lib/context.js:150:16)
remote: at TraversalContext.visitSingle (/tmp/build_43fb00b7ca544651b6eb4730c0d0ad94/node_modules/babel-traverse/lib/context.js:108:19)
remote: at TraversalContext.visit (/tmp/build_43fb00b7ca544651b6eb4730c0d0ad94/node_modules/babel-traverse/lib/context.js:192:19)
remote: at Function.traverse.node (/tmp/build_43fb00b7ca544651b6eb4730c0d0ad94/node_modules/babel-traverse/lib/index.js:114:17)
remote: at NodePath.visit (/tmp/build_43fb00b7ca544651b6eb4730c0d0ad94/node_modules/babel-traverse/lib/path/context.js:115:19)
```
This throws when the page it is saying at fault does not even use any of the variables supposed to be defined in env, but simply uses Unary Expression like "typeof".

Perhaps make the error clearer if the env passed in .babelrc is returning {} or null?

Thanks