Users cannot deprecate entries with sale agents that lack authority records

[demery]

When users attempt to deprecate entries with sale agents who have an observed name but no authority record, an exception is raised:

A NoMethodError occurred in entries#deprecate:

 undefined method `id' for nil:NilClass
 app/models/entry.rb:221:in `block in decrement_counters'
 app/models/entry.rb:220:in `each'
 app/models/entry.rb:220:in `decrement_counters'
 app/controllers/entries_controller.rb:538:in `block in deprecate'
 app/controllers/entries_controller.rb:495:in `deprecate'

The problem occurs here:

https://github.com/upenn-libraries/sdbmss/blob/master/app/models/entry.rb#L219-L224

    if sale
      sale.sale_agents.map(&:agent).uniq.each do |sale_agent|
        Name.decrement_counter(:sale_agents_count, sale_agent.id)
        objects.push(sale_agent)
      end
    end

The problem occurred with SDBM_ 8263, which has sale agents below. Note that the agent with observed_name 'Llewellyn' has a null agent_id.

mysql> select * from sale_agents where sale_id = 8257;
+--------+---------+---------------+----------+------------------+---------------------+---------------------+---------------------+------------------------+
| id     | sale_id | observed_name | agent_id | role             | created_at          | updated_at          | uncertain_in_source | supplied_by_data_entry |
+--------+---------+---------------+----------+------------------+---------------------+---------------------+---------------------+------------------------+
|  12068 |    8257 | NULL          |     7322 | selling_agent    | NULL                | NULL                |                   0 |                      0 |
|  12069 |    8257 | NULL          |    12621 | seller_or_holder | NULL                | NULL                |                   0 |                      0 |
| 160151 |    8257 | Llewellyn     |     NULL | buyer            | 2020-02-03 20:20:44 | 2020-02-03 20:20:44 |                   0 |                      0 |
+--------+---------+---------------+----------+------------------+---------------------+---------------------+---------------------+------------------------+

The problem can be corrected by skipping agents without an agent_id:

    if sale
      sale.sale_agents.map(&:agent).uniq.each do |sale_agent|
        next if sale_agent.blank? # skip if agent_id is null <= Add this line
        Name.decrement_counter(:sale_agents_count, sale_agent.id)
        objects.push(sale_agent)
      end
    end