fix(Select): support array value when using multiple

[prescottprue]

Issue

Using multiple option with Select like so:

<FormControl>
  <InputLabel htmlFor="some">My Field</InputLabel>
  <Field
    name={name}
    component={Select}
    fullWidth
    name="some"
    placeholder="Select Some Items">
      <MenuItem value={10}>Ten</MenuItem>
      <MenuItem value={20}>Twenty</MenuItem>
      <MenuItem value={30}>Thirty</MenuItem>
    ))}
  </Field>
</FormControl>

Produces the following error:

The exact message is:

Uncaught Error: Material-UI: the `value` property must be an array when using the `Select` component with `multiple`.`

Dependencies Versions

For those trying to replicate, here are my dependencies versions

• redux-form-material-ui - 5.0.0-beta.3
• @material-ui/core - 3.0.0
• react + react-dom - ^16.3.0

Solution

If the value is not an array and props.multiple is enabled, an empty array is returned. This handles the case of a SelectField that has multiple

[codecov]

Codecov Report

Merging #277 into 5.0 will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              5.0     #277   +/-   ##
=======================================
  Coverage   66.66%   66.66%           
=======================================
  Files           8        8           
  Lines          24       24           
=======================================
  Hits           16       16           
  Misses          8        8

Impacted Files	Coverage Δ
src/Select.js	20% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9328e93...77a603f. Read the comment docs.