TypeScript: MappingItem.source can be null

[nikolay-borzov]

There is a check in the code

 this._wasm.withMappingCallback(
      mapping => {
        if (mapping.source !== null) {
          mapping.source = this._absoluteSources.at(mapping.source);

          if (mapping.name !== null) {
            mapping.name = this._names.at(mapping.name);
          }
        }
        if (this._computedColumnSpans && mapping.lastGeneratedColumn === null) {
          mapping.lastGeneratedColumn = Infinity;
        }

        aCallback.call(context, mapping);
      },

therefore source can be null

create-react-app main.*.chunk,js.map contains null source

[coveralls]

Pull Request Test Coverage Report for Build 577

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 88.713%

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Totals
Change from base Build 576:	0.0%
Covered Lines:	2481
Relevant Lines:	2733

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 577

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 88.713%

---

Totals
Change from base Build 576:	0.0%
Covered Lines:	1654
Relevant Lines:	1822

---

💛 - Coveralls