Using Formik and Yup, how to have no default for a numeric field

I'm using Formik and Yup. I can't figure out how I can specify a numeric field with no default?

Here are my validations:

 const initialValues: any = {
    string: "",
    numeric1: undefined,
    numeric2: ""
  };

  const validationSchema = yup.object().shape({
    string: yup.string().required("Required"),
    numeric1: yup.string().required("Required (numeric type)"),
    numeric2: yup.number().required("Required (string type)")
  });

Numeric1 is type=number and Numeric2 is type=text

If I specify a number type

            <Form.Group className="mb-0" controlId="numeric1">
              <Form.Label className="required">Number of users</Form.Label>
              <Form.Control
                type="number"
                placeholder="Enter number (numeric type)"
                {...getFieldProps("numeric1")}
                isInvalid={touched.numeric1 && !!errors.numeric1}
                isValid={touched.numeric1 && !errors.numeric1}
              />
              <Form.Control.Feedback type="invalid">
                {touched.numeric1 && errors.numeric1}
              </Form.Control.Feedback>
            </Form.Group>

I make the initial value Undefined, but then React complains that because the initial value can't be undefined A component is changing an uncontrolled input to be controlled. This is likely caused by the value changing from undefined to a defined value, which should not happen.

If I specify a text type

            <Form.Group className="mb-0" controlId="numeric2">
              <Form.Label className="required">Number of users</Form.Label>
              <Form.Control
                type="string"
                placeholder="Enter number (string type)"
                {...getFieldProps("numeric2")}
                isInvalid={touched.numeric2 && !!errors.numeric2}
                isValid={touched.numeric2 && !errors.numeric2}
              />
              <Form.Control.Feedback type="invalid">
                {touched.numeric2 && errors.numeric2}
              </Form.Control.Feedback>
            </Form.Group>

Then I get an unfriendly error message if I try to specify letters, because the Yup validation gets a NaN.

Code is here: https://codesandbox.io/s/numeric-validations-h50gg If you enter something like 'abc' in the numeric fields, you'll see what I mean (open the console log as well)

What is the best way to not have to specify a default for a numeric field?