Fixing the wp_editor error in WordPress 3.9

correct-wp_editor-method.php

/**
 * This is the correct method of using wp_editor()
 **/
// Codex usage:
wp_editor( $content, $editor_id, $settings = array() );

// Example of proper use in a widget
wp_editor( 'content', 'content', array( 'textarea_name' => $this->get_field_id( 'content' ), ) );

// Alternate method when get_field_id is not available (options page or other)
// Change settings_field_name[content] to the correct settings field and field name
wp_editor( 'content', 'content', array( 'textarea_name' => 'settings_field_name[content]' ), ) );

original-bad-method.php

/**
 * This is how NOT to do it
 **/
// Codex usage:
wp_editor( $content, $editor_id, $settings = array() );

// Example of inproper use (in a widget)
wp_editor( 'content', $this->get_field_id( 'content' ) );

// Example of inproper use elsewhere
// Change settings_field_name[content] to the correct settings field and field name
wp_editor( 'content', 'settings_field_name[content]' ) );