TypeError: fileTimestamps.get is not a function

[felixfbecker]

I am getting this error when using this plugin, webpack 4.15.1

node_modules/webpack/lib/NormalModule.js:513
                        const timestamp = fileTimestamps.get(file);
                                    ^
TypeError: fileTimestamps.get is not a function
    at NormalModule.needRebuild (node_modules/webpack/lib/NormalModule.js:513:37)
    at Compilation.addModule (node_modules/webpack/lib/Compilation.js:518:27)
    at moduleFactory.create (node_modules/webpack/lib/Compilation.js:962:35)
    at factory (node_modules/webpack/lib/NormalModuleFactory.js:405:6)
    at hooks.afterResolve.callAsync (node_modules/webpack/lib/NormalModuleFactory.js:155:13)
    at AsyncSeriesWaterfallHook.eval [as callAsync] (eval at create (node_modules/tapable/lib/HookCodeFactory.js:24:12), <anonymous>:6:1)
    at AsyncSeriesWaterfallHook.lazyCompileHook [as _callAsync] (node_modules/tapable/lib/Hook.js:35:21)
    at resolver (node_modules/webpack/lib/NormalModuleFactory.js:138:29)
    at process.nextTick (node_modules/webpack/lib/NormalModuleFactory.js:342:9)
    at process._tickCallback (internal/process/next_tick.js:61:11)