angular-cli: TypeError: Cannot read property 'length' of undefined, when karma tests re-load

This bug report is from using Angular2 and Karma/Jasmine But the error is emitted from Typescript. I am hoping that is the relevant part.

Versions

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  / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | |
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/_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|
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Angular CLI: 1.6.5
Node: 8.7.0
OS: darwin x64
Angular: 4.3.6
... animations, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, router, tsc-wrapped

@angular/.DS_Store: error
@angular/cli: 1.6.5
@angular-devkit/build-optimizer: 0.0.41
@angular-devkit/core: 0.0.28
@angular-devkit/schematics: 0.0.51
@ngtools/json-schema: 1.1.0
@ngtools/webpack: 1.9.5
@schematics/angular: 0.1.16
typescript: 2.3.4
webpack-bundle-analyzer: 2.9.2
webpack: 3.10.0

----
Some more versions that might be helpful

        "jasmine-core": "^2.99.1",
        "jasmine-expect": "^3.8.3",
        "jasmine-matchers": "^0.2.3",
        "jasmine-spec-reporter": "~4.1.0",
        "karma": "~1.7.0",
        "karma-chrome-launcher": "^2.2.0",
        "karma-cli": "~1.0.1",
        "karma-coverage-istanbul-reporter": "^1.2.1",
        "karma-jasmine": "^1.1.1",
        "karma-jasmine-html-reporter": "^0.2.2",
        "karma-jasmine-matchers": "^3.7.0",

I am using macOS Sierra, 10.12.6

Repro steps

When I run $ npm run test, my tests pass fine.
But if I then save one of my spec files (even if I don’t change it) Then a new run is kicked off, but always produces this error:

Observed behavior

ERROR in TypeError: Cannot read property 'length' of undefined
    at createSourceFile (/Users/jschank/ddc-advocacy/projects/ddca-iceland/node_modules/typescript/lib/typescript.js:15464:110)
    at parseSourceFileWorker (/Users/jschank/ddc-advocacy/projects/ddca-iceland/node_modules/typescript/lib/typescript.js:15389:26)
    at Object.parseSourceFile (/Users/jschank/ddc-advocacy/projects/ddca-iceland/node_modules/typescript/lib/typescript.js:15338:26)
    at Object.createSourceFile (/Users/jschank/ddc-advocacy/projects/ddca-iceland/node_modules/typescript/lib/typescript.js:15192:29)
    at new TypeScriptFileRefactor (/Users/jschank/ddc-advocacy/projects/ddca-iceland/node_modules/@ngtools/webpack/src/refactor.js:79:35)
    at Object.findLazyRoutes (/Users/jschank/ddc-advocacy/projects/ddca-iceland/node_modules/@ngtools/webpack/src/lazy_routes.js:18:22)
    at AotPlugin._findLazyRoutesInAst (/Users/jschank/ddc-advocacy/projects/ddca-iceland/node_modules/@ngtools/webpack/src/plugin.js:217:50)
    at _donePromise.Promise.resolve.then.then.then.then.then (/Users/jschank/ddc-advocacy/projects/ddca-iceland/node_modules/@ngtools/webpack/src/plugin.js:496:24)
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:188:7)

Desired behavior

Saving my spec files should result in karma tests being run again. (I know that isn’t the responsibility of this repo. But the error Appears to me to be in Typescript)

Mention any other details that might be useful (optional)

Most of the googling about this error, leads to the advice of putting a console.log(fileName); statement. To dump the offending file to the console. When I look at that location, I see this

function createSourceFile(fileName, languageVersion, scriptKind) {
	// code from createNode is inlined here so createNode won't have to deal with special case of creating source files
	// this is quite rare comparing to other nodes and createNode should be as fast as possible
	var sourceFile = new SourceFileConstructor(265 /* SourceFile */, /*pos*/ 0, /* end */ sourceText.length);
	nodeCount++;
	sourceFile.text = sourceText;
	sourceFile.bindDiagnostics = [];
	sourceFile.languageVersion = languageVersion;
	sourceFile.fileName = ts.normalizePath(fileName);
	sourceFile.languageVariant = getLanguageVariant(scriptKind);
	sourceFile.isDeclarationFile = ts.fileExtensionIs(sourceFile.fileName, ".d.ts");
	sourceFile.scriptKind = scriptKind;
	return sourceFile;
}

It looks to me, like the problem is that sourceText, is undefined. And we’re calling length on it here.
If I reset the sourceText to an empty string, when it is undefined or null. My tests re-run on changes, with no errors. Unfortunately, I have no idea if that is a reasonable solution to the problem.

function createSourceFile(fileName, languageVersion, scriptKind) {
	if (!sourceText) {
		// console.log("*** Filename: ", fileName);
		// console.log("*** languageVersion: ", languageVersion);
		// console.log("*** scriptKind: ", scriptKind);
		// Note: this seems to allow the typescript parser to continue when a file is updated
		sourceText = "";
	}
	// code from createNode is inlined here so createNode won't have to deal with special case of creating source files
	// this is quite rare comparing to other nodes and createNode should be as fast as possible
	var sourceFile = new SourceFileConstructor(265 /* SourceFile */, /*pos*/ 0, /* end */ sourceText.length);
	nodeCount++;
	sourceFile.text = sourceText;
	sourceFile.bindDiagnostics = [];
	sourceFile.languageVersion = languageVersion;
	sourceFile.fileName = ts.normalizePath(fileName);
	sourceFile.languageVariant = getLanguageVariant(scriptKind);
	sourceFile.isDeclarationFile = ts.fileExtensionIs(sourceFile.fileName, ".d.ts");
	sourceFile.scriptKind = scriptKind;
	return sourceFile;
}