How to use the @nivo/circle-packing.BubbleDefaultProps.identity function in @nivo/circle-packing

description: 'The hierarchical data object.',
        type: '{Object}',
        required: true,
    },
    {
        key: 'identity',
        description: (
            <span>
                define value accessor, if string given, will use <code>datum[value]</code>,<br>
                if function given, it will be invoked for each node and will receive the node as
                first argument, it must return the node value.
            </span>
        ),
        type: '{string|Function}',
        required: false,
        default: defaults.identity,
    },
    {
        key: 'value',
        description: (
            <span>
                define value accessor, if string given, will use <code>datum[value]</code>,<br>
                if function given, it will be invoked for each node and will receive the node as
                first argument, it must return the node value.
            </span>
        ),
        type: '{string|Function}',
        required: false,
        default: 'value',
    },
    {
        key: 'width',

type: 'object',
        required: true,
        group: 'Base',
    },
    {
        key: 'identity',
        help: 'Define id accessor.',
        description: `
            define id accessor, if string given, will use
            \`datum[value]\`, if function given, it will be
            invoked for each node and will receive the node as
            first argument, it must return the node value.
        `,
        type: 'string | Function',
        required: false,
        defaultValue: defaults.identity,
        group: 'Base',
    },
    {
        key: 'value',
        help: 'Define value accessor.',
        description: `
            define value accessor, if string given, will use
            \`datum[value]\`, if function given, it will be
            invoked for each node and will receive the node as
            first argument, it must return the node value.
        `,
        type: 'string | Function',
        required: false,
        defaultValue: 'value',
        group: 'Base',
    },