WordPress script for doing a .csv export of misc data

bbg-csv-export.php

<?php

function bbg_csv_export() {
	if ( ! is_super_admin() ) {
		return;
	}

	if ( ! isset( $_GET['bbg_export'] ) ) {
		return;
	}

	$filename = 'mcnrc-members-' . time() . '.csv';

	$header_row = array(
		0 => 'Display Name',
		1 => 'Email',
		2 => 'Institution',
		3 => 'Registration Date',
	);

	$data_rows = array();

	global $wpdb, $bp;
	$users = $wpdb->get_results( "SELECT ID, user_email, user_registered FROM {$wpdb->users} WHERE user_status = 0" );

	foreach ( $users as $u ) {
		$row = array();
		$row[0] = bp_core_get_user_displayname( $u->ID );
		$row[1] = $u->user_email;
		$row[2] = xprofile_get_field_data( 2, $u->ID );
		$row[3] = $u->user_registered;

		$data_rows[] = $row;
	}

	$fh = @fopen( 'php://output', 'w' );

	fprintf( $fh, chr(0xEF) . chr(0xBB) . chr(0xBF) );

	header( 'Cache-Control: must-revalidate, post-check=0, pre-check=0' );
	header( 'Content-Description: File Transfer' );
	header( 'Content-type: text/csv' );
	header( "Content-Disposition: attachment; filename={$filename}" );
	header( 'Expires: 0' );
	header( 'Pragma: public' );

	fputcsv( $fh, $header_row );

	foreach ( $data_rows as $data_row ) {
		fputcsv( $fh, $data_row );
	}

	fclose( $fh );
	die();
}
add_action( 'admin_init', 'bbg_csv_export' );

Fatal error: Uncaught TypeError: fputcsv(): Argument #2 ($fields) must be of type array, string given in