react-jsonschema-forms validator error - Cannot read properties of undefined (reading 'replace')

I'm trying to build dynamic forms using rjsf and having some issues with the validator.

This corresponds to this line in the code:

var property = instancePath.replace(/\//g, ".");

My schema is:

const testSchema = {
    "type": "object",
    "required": [
        "account",
    ],
    "properties": {
        "reference": {
            "type": "string",
            "description": "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua",
            "nullable": true,
        },
        "account": {
            "type": "integer",
            "format": "int64",
            "pattern":"^(0|[1-9][0-9]*)$",
        }
    },

    "additionalProperties": false
};

import Form from "@rjsf/bootstrap-4";
import validator from "@rjsf/validator-ajv8";

return <>
    { schema && <Form 
        schema={testSchema}
        uiSchema={uiSchema}
        validator={validator}
        onSubmit={onSubmit}
        noHtml5Validate={true}
        formData={formData}
        onChange={(e)=> onChangeHandler(e.formData)}
    />}</>;