Bench start faild error

when i try bench start

internal/validators.js:125
 16:04:51 watch.1          |     throw new ERR_INVALID_ARG_TYPE(name, 'string', value);
16:04:51 watch.1          |     ^
16:04:51 watch.1          | 
 16:04:51 watch.1          | TypeError [ERR_INVALID_ARG_TYPE]: The      "path" argument must be of type string. Received type undefined
16:04:51 watch.1          |     at validateString (internal/validators.js:125:11)

16:04:51 watch.1 | at Object.resolve (path.js:1080:7)
16:04:51 watch.1 | at get_rollup_options_for_css (/home/omar/frappe-bench/apps/frappe/rollup/config.js:123:12)
16:04:51 watch.1 | at get_rollup_options (/home/omar/frappe-bench/apps/frappe/rollup/config.js:31:10)
16:04:51 watch.1 | at Object.keys.map.output_file (/home/omar/frappe-bench/apps/frappe/rollup/config.js:174:5)
16:04:51 watch.1 | at Array.map ()
16:04:51 watch.1 | at get_options_for (/home/omar/frappe-bench/apps/frappe/rollup/config.js:162:4)
16:04:51 watch.1 | at get_watch_options (/home/omar/frappe-bench/apps/frappe/rollup/watch.js:57:18)
16:04:51 watch.1 | at apps_list.map.app (/home/omar/frappe-bench/apps/frappe/rollup/watch.js:21:24)
16:04:51 watch.1 | at Array.map ()
16:04:51 watch.1 | at watch_assets (/home/omar/frappe-bench/apps/frappe/rollup/watch.js:20:12)
16:04:51 watch.1 | at Object. (/home/omar/frappe-bench/apps/frappe/rollup/watch.js:16:1)
16:04:51 watch.1 | at Module._compile (internal/modules/cjs/loader.js:778:30)
16:04:51 watch.1 | at Object.Module._extensions…js
(internal/modules/cjs/loader.js:789:10)
16:04:51 watch.1 | at Module.load (internal/modules/cjs/loader.js:653:32)
16:04:51 watch.1 | at tryModuleLoad (internal/modules /cjs/loader.js:593:12)
16:04:51 watch.1 | error Command failed with exit code 1.

16:04:51 watch.1 | info Visit https://yarnpkg.com/en/docs /cli/run for documentation about this command.

would you tell us more details about installation process