[Bug Report] el-select: input disappears when value of select is a new object

[tkmikan]

Element UI version

2.4.5

OS/Browsers version

Win10/1803(17134.191) Chrome/67.0.3396.62

Vue version

2.5.17

Reproduction Link

https://jsfiddle.net/jdfL6bse/

Steps to reproduce

• value is a new object (that is, using value="item" and adjust the value-key in the example above will NOT lead to the problem)
• appears only in single select and when custom filter-method is provided
• type any letter that matches the filter-method, and your input disappears

What is Expected?

don't clear my input

just want to have the same behavior as the select value is a Number or something

What is actually happening?

anything you type disappears, except:

1. the input doesn't match any options, thus the filteredlist is an empty array
2. the input is exactly the same as what has just disappeared (perhaps it is previousQuery === query)