problem installing ralph - gulp

./node_modules/.bin/gulp
assert.js:375
throw err;
^

AssertionError [ERR_ASSERTION]: Task function must be specified
at Gulp.set [as _setTask] (/opt/ralph/ralph-20190627.1/node_modules/undertaker/lib/set-task.js:10:3)
at Gulp.task (/opt/ralph/ralph-20190627.1/node_modules/undertaker/lib/task.js:13:8)
at Object. (/opt/ralph/ralph-20190627.1/gulpfile.js:140:6)
at Module._compile (internal/modules/cjs/loader.js:776:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:787:10)
at Module.load (internal/modules/cjs/loader.js:643:32)
at Function.Module._load (internal/modules/cjs/loader.js:556:12)
at Module.require (internal/modules/cjs/loader.js:683:19)
at require (internal/modules/cjs/helpers.js:16:16)
at execute (/opt/ralph/ralph-20190627.1/node_modules/gulp/node_modules/gulp-cli/lib/versioned/^4.0.0/index.js:36:18) {
generatedMessage: false,
code: 'ERR_ASSERTION',
actual: false,
expected: true,
operator: '=='
}

gulp -v
CLI version: 2.2.0
Local version: 4.0.2

node -v
v12.6.0