TypeError: Cannot call method 'substr' of undefined

[wmr...@cloudpassage.com]

I can't seem to wrap my head around this error: TypeError: Cannot call method 'substr' of undefined in lib/source-map/source-node.js:94:33

It's as if the code in source-node.js is shifting one too many elements in the source array.

The full stack trace is here:

/Users/wmruzek/cp/dev/cpclient/node_modules/webpack/node_modules/webpack-core/lib/NormalModuleMixin.js:161
if(isError) throw e;
^
TypeError: Cannot call method 'substr' of undefined
at Function.<anonymous> (/Users/wmruzek/cp/dev/cpclient/node_modules/webpack/node_modules/webpack-core/node_modules/source-map/lib/source-map/source-node.js:94:33)
at Array.forEach (native)
at SourceMapConsumer_eachMapping [as eachMapping] (/Users/wmruzek/cp/dev/cpclient/node_modules/webpack/node_modules/webpack-core/node_modules/source-map/lib/source-map/source-map-consumer.js:478:10)
at Function.SourceNode_fromStringWithSourceMap [as fromStringWithSourceMap] (/Users/wmruzek/cp/dev/cpclient/node_modules/webpack/node_modules/webpack-core/node_modules/source-map/lib/source-map/source-node.js:78:26)
at Source.OriginalSource (/Users/wmruzek/cp/dev/cpclient/node_modules/webpack/node_modules/webpack-core/lib/OriginalSource.js:39:21)
at DependenciesBlock.onModuleBuild (/Users/wmruzek/cp/dev/cpclient/node_modules/webpack/node_modules/webpack-core/lib/NormalModuleMixin.js:279:19)
at nextLoader (/Users/wmruzek/cp/dev/cpclient/node_modules/webpack/node_modules/webpack-core/lib/NormalModuleMixin.js:253:25)
at /Users/wmruzek/cp/dev/cpclient/node_modules/webpack/node_modules/webpack-core/lib/NormalModuleMixin.js:270:15
at Object.context.callback (/Users/wmruzek/cp/dev/cpclient/node_modules/webpack/node_modules/webpack-core/lib/NormalModuleMixin.js:146:14)
at Object.module.exports (/Users/wmruzek/cp/dev/cpclient/node_modules/6to5-loader/index.js:23:10)

I put an issue in the repo here. No response yet.
https://github.com/mozilla/source-map/issues/138