TypeError when the rules are an empty string

[lerit]

Versions:

• VueJs: 2..4.2
• Vee-Validate:2.0.0-rc.8

Description:

<textarea name="myField" v-validate="checked ? 'required|alpha' : ''"> it work before(rc.7),after update to rc.8,it throw error: "Error in directive validate bind hook: "TypeError: Cannot convert undefined or null to object"" after debug,i find error throw in Field.prototype.updateDependencies ,when try to read this.rules ### Steps To Reproduce: https://jsfiddle.net/gcnf5ucn/8/

[lerit]

my reproduce is base on this link:#622,
in that issue,logaretm give a example ,and it work fine(base on rc.5)

[logaretm]

It works fine, but it seems like it breaks if you provide an empty rules string to it:

https://jsfiddle.net/logaretm/gcnf5ucn/9/