fix: handle undefined sourcesContent and null sourcesContent entry

lib/source.js

@@ -4,7 +4,7 @@ const { GREATEST_LOWER_BOUND, LEAST_UPPER_BOUND } = require('source-map').Source
 
 module.exports = class CovSource {
   constructor (sourceRaw, wrapperLength) {
-    sourceRaw = sourceRaw.trimEnd()
+    sourceRaw = sourceRaw ? sourceRaw.trimEnd() : ''
     this.lines = []
     this.eof = sourceRaw.length
     this.shebangLength = getShebangLength(sourceRaw)

lib/v8-to-istanbul.js

@@ -1,5 +1,7 @@
 const assert = require('assert')
 const convertSourceMap = require('convert-source-map')
+const util = require('util')
+const debuglog = util.debuglog('c8')
 const { dirname, isAbsolute, join, resolve } = require('path')
 const { fileURLToPath } = require('url')
 const CovBranch = require('./branch')
@@ -52,6 +54,9 @@ module.exports = class V8ToIstanbul {
     if (this.rawSourceMap) {
       if (this.rawSourceMap.sourcemap.sources.length > 1) {
         this.sourceMap = await new SourceMapConsumer(this.rawSourceMap.sourcemap)
+        if (!this.sourceMap.sourcesContent) {
+          this.sourceMap.sourcesContent = await this.sourcesContentFromSources()
+        }
         this.covSources = this.sourceMap.sourcesContent.map((rawSource, i) => ({ source: new CovSource(rawSource, this.wrapperLength), path: this.sourceMap.sources[i] }))
         this.sourceTranspiled = new CovSource(rawSource, this.wrapperLength)
       } else {
@@ -84,6 +89,18 @@ module.exports = class V8ToIstanbul {
     }
   }
 
+  async sourcesContentFromSources () {
+    const fileList = this.sourceMap.sources.map(relativePath => {
+      const realPath = this._resolveSource(this.rawSourceMap, relativePath)
+      return readFile(realPath, 'utf-8')
+        .then(result => result)
+        .catch(err => {
+          debuglog(`failed to load ${realPath}: ${err.message}`)
+        })
+    })
+    return await Promise.all(fileList)
+  }
+
   destroy () {
     if (this.sourceMap) {
       this.sourceMap.destroy()