Add nullableMorphs in migrations

[antonkomarev]

I don't know how to better describe that fields will be nullable:

Adds unsigned INTEGER `taggable_id` NULL and STRING `taggable_type` NULL

Or:

Adds nullable unsigned INTEGER `taggable_id` and nullable STRING `taggable_type`

[tillkruss]

You could even shorten it to.

Same as `morphs()`.

Same as nullableTimestamps() does.

[antonkomarev]

It's not the same. Because nullableMorphs() generates nullable columns and morphs() generates not nullable columns. So it's not just an alias.

public function morphs($name, $indexName = null)
{
    $this->unsignedInteger("{$name}_id");

    $this->string("{$name}_type");

    $this->index(["{$name}_id", "{$name}_type"], $indexName);
}

public function nullableMorphs($name, $indexName = null)
{
    $this->unsignedInteger("{$name}_id")->nullable();

    $this->string("{$name}_type")->nullable();

    $this->index(["{$name}_id", "{$name}_type"], $indexName);
}

And nullableTimestamps marked as same as timestamps in docs because they have same output result.

public function nullableTimestamps()
{
    $this->timestamps();
}