React Hook Forms + Material UI Checkboxes

I am having an error when submiting a form build using React Hook Form and material-ui checkboxes components. The number of checkboxes are build from a list from my api:

        <Grid item xs={12}>
          <FormControl
            required
            error={errors.project?.stack ? true : false}
            component='fieldset'>
            <FormLabel component='legend'>Tech Stack</FormLabel>
            <FormGroup>
              <Grid container spacing={1}>
                {techs.map((option, i) => (
                  <Grid item xs={4} key={i}>
                    <FormControlLabel
                      control={
                        <Checkbox
                          id={`stack${i}`}
                          name='project.stack'
                          value={option.id}
                          inputRef={register({required: 'Select project Tech Stack'})}
                        />
                      }
                      label={option.name}
                    />
                  </Grid>
                ))}
              </Grid>
            </FormGroup>
            <FormHelperText>{errors.project?.stack}</FormHelperText>
          </FormControl>
        </Grid>

When the form is submited I got the following error ( several times , 1 for each checkbox rendered ) :

Uncaught (in promise) Error: Objects are not valid as a React child (found: object with keys {type, message, ref}). If you meant to render a collection of children, use an array instead.

I don't understand this error. The message apparently says it is a rendering issue, but the component renders fine. The problems happens on submit. Any advices ?

Thank you

Solution 1:

UPDATE: if you are using RHF >= 7, you should use props.field to call props.field.value and props.field.onChange.

You can use the default Checkbox Controller:

<FormControlLabel
    control={
      <Controller
        name={name}
        control={control}
        render={(props) => (
          <Checkbox
            {...props}
            checked={props.value}
            onChange={(e) => props.onChange(e.target.checked)}
          />
        )}
      />
    }
    label={label}
  />

I used the controller example from RHF but had to add checked={props.value}: https://github.com/react-hook-form/react-hook-form/blob/master/app/src/controller.tsx

Solution 2:

I managed to make it work without using Controller. The props should be inside the FormControlLabel and not inside Checkbox

                <Grid item xs={4} key={i}>
                    <FormControlLabel
                      value={option.id}
                      control={<Checkbox />}
                      label={option.name}
                      name={`techStack[${option.id}]`}
                      inputRef={register}
                    />
                  </Grid>
                ))}