must use `entry` when set `title`

[chiaweilee]

Version

3.0.5

Node and OS info

Node 8.12

Steps to reproduce

// vue.config.js
module.exports = {
  pages: {
    index: {
      // entry: 'src/main.js' // Error if without 'entry'
      title: 'title here'
    }
  }
}

TypeError: Path must be a string. Received undefined
TypeError: Path must be a string. Received undefined

What is expected?

• use default if entry set is undefined

What is actually happening?

• Intent to change a title
• Intent to use default entry without set
• And an error told you that you must set entry

[haoqunjiang]

It is documented:

An object that specifies its entry, template, filename, title and chunks (all optional except entry);

Nonetheless, the error message could be improved by revising the vue.config.js options schema.