UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside

[ppttfish]

(node:4968) [DEP_WEBPACK_DEPRECATION_ARRAY_TO_SET_LENGTH] DeprecationWarning: Compilation.modules was changed from Array to Set (using Array property 'length' is deprecated)
(node:4968) [DEP_WEBPACK_DEPRECATION_ARRAY_TO_SET_INDEXER] DeprecationWarning: Compilation.modules was changed from Array to Set (indexing Array is deprecated)
(node:4968) UnhandledPromiseRejectionWarning: TypeError: Cannot convert undefined or null to object
at Function.from ()
at D:\data\webpack-demo\test\node_modules\fontmin-webpack\lib\index.js:47:32
at arrayMap (D:\data\webpack-demo\test\node_modules\lodash\lodash.js:639:23)
at Function.map (D:\data\webpack-demo\test\node_modules\lodash\lodash.js:9580:14)
at interceptor (D:\data\webpack-demo\test\node_modules\lodash\lodash.js:17046:35)
at Function.thru (D:\data\webpack-demo\test\node_modules\lodash\lodash.js:8817:14)
at D:\data\webpack-demo\test\node_modules\lodash\lodash.js:4388:28
at arrayReduce (D:\data\webpack-demo\test\node_modules\lodash\lodash.js:683:21)
at baseWrapperValue (D:\data\webpack-demo\test\node_modules\lodash\lodash.js:4387:14)
at LodashWrapper.wrapperValue (D:\data\webpack-demo\test\node_modules\lodash\lodash.js:9072:14)
(node:4968) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside
of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag --unhandled-rejections=strict (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:4968) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

webpack.config.js
plugins: [
new FontminPlugin({
glyphs: ['明月']
})
]

what should i do

[patrickhulce]

Thanks for filing @ppttfish! Are you using this with webpack 5?

[patrickhulce]

f306975 converts this to a warning instead of a fatal error, but if you are using v5 and can provide a full webpack config that repros this failure I'm happy to take another look :)