declaration-bundler-webpack-plugin.fix.js

const DeclarationBundlerPlugin = require("declaration-bundler-webpack-plugin");

let buggyFunc = DeclarationBundlerPlugin.prototype.generateCombinedDeclaration;
DeclarationBundlerPlugin.prototype.generateCombinedDeclaration = function (
  declarationFiles
) {
  for (var fileName in declarationFiles) {
    let declarationFile = declarationFiles[fileName];
    declarationFile._value = declarationFile._value || declarationFile.source();
  }
  return buggyFunc.call(this, declarationFiles);
};

module.exports = DeclarationBundlerPlugin;