Fatal error: Call to undefined function wp_get_current_user()

I have some strange error or may be I do not have the skills to tackle this issue.
I am building a plugin for Multisite. When is use is_admin(), my plugin works fine but when I use is_super_admin it shows me this error Fatal error: Call to undefined function wp_get_current_user(). I did my search but could not be able to find any solution.

My Code is this

if(!is_super_admin()){
    add_action('widgets_init','my_unregister_widdget');
    function my_unregister_widgets() {
        unregister_widget( 'WP_Widget_Pages' );
        unregister_widget( 'WP_Widget_Calendar' );
    }
}

I saw this question but it’s not helping me.

Answers:

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Method 1

wp_get_current_user() is a pluggable function and not yet available when your plugin is included. You have to wait for the action plugins_loaded:

Example:

add_action( 'plugins_loaded', 'wpse_92517_init' );

function wpse_92517_init()
{
    if(!is_super_admin())
        add_action('widgets_init','my_unregister_widget');
}

function my_unregister_widgets() {
    unregister_widget( 'WP_Widget_Pages' );
    unregister_widget( 'WP_Widget_Calendar' );
}

Or move the check into the widget function:

add_action( 'widgets_init', 'my_unregister_widget' );

function my_unregister_widgets() 
{
    if ( is_super_admin() )
        return;

    // not super admin
    unregister_widget( 'WP_Widget_Pages' );
    unregister_widget( 'WP_Widget_Calendar' );
}

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0