Fix possible null return from views_handler_field_field::get_base_table()

[laryn]

Description of the bug

I'm troubleshooting exceptions in various tests for a custom module, where the base table being returned from views_handler_field_field::get_base_table() is null. These are for views with relationships via entityreference, for "Content referencing content from ..." and the resulting pseudofield names are in the form reverse_{field_name}_{entity_type}.

The following section of code is returning null:

  /**
   * Set the base_table and base_table_alias.
   *
   * @return string
   *   The base table which is used in the current view "context".
   */
  function get_base_table() {
    if (!isset($this->base_table)) {
      // This base_table is coming from the entity not the field.
      $this->base_table = $this->view->base_table;

      // If the current field is under a relationship you can't be sure that the
      // base table of the view is the base table of the current field.
      // For example a field from a node author on a node view does have users as base table.
      if (!empty($this->options['relationship']) && $this->options['relationship'] != 'none') {
        $relationships = $this->view->display_handler->get_option('relationships');
        if (!empty($relationships[$this->options['relationship']])) {
          $options = $relationships[$this->options['relationship']];
          $data = views_fetch_data($options['table']);
          $this->base_table = $data[$options['field']]['relationship']['base'];
        }
      }
    }

    return $this->base_table;
  }

The docblock indicates that a string should be returned, so I am thinking that if no base_table string is returned in the last if section, we keep the base table value from the entity instead of returning null. Is that reasonable?

[avpaderno]

On the shown code, $this->base_table is set twice.

// This base_table is coming from the entity not the field.
$this->base_table = $this->view->base_table;

$data = views_fetch_data($options['table']);
$this->base_table = $data[$options['field']]['relationship']['base'];

How can the code be sure $data[$options['field']]['relationship']['base'] is preferable to $this->view->base_table?

[argiepiano]

It would be helpful to get steps to reproduce. I've never seen this issue with entity reference fields.