[PATCH] Don't attempt to add null objects to a JsonArray in RequestProcessor

[taylor.smock]

For some reason, on some configurations, my plugin isn't registering itself properly, which causes an NPE in RequestProcessor#getHandlersInfoAsJson. This is due to the code returning a null value (on purpose), and then attempting to add the null value to the JsonArray builder.

This is a regression from r16550. StringBuilder happily accepted null values and output null in the string.

I'm attaching a partial preferences xml so I can fix it in MapWithAI as well (I shouldn't be allowing 8111 ports in mapwithai.sources.entries right now).

  <tag key='remotecontrol.enabled' value='true'/>
  <tag key='remotecontrol.new-layer' value='true'/>
  <maps key='mapwithai.sources.entries'>
    <map>
      <tag key='parameters' value='[]'/>
      <tag key='name' value='a'/>
      <tag key='type' value='thirdParty'/>
      <tag key='url' value='http://localhost:8111/features?q=mapwithai'/>
      <tag key='cookies' value=''/>
      <tag key='customHttpHeaders' value='{}'/>
      <tag key='category' value='other'/>
    </map>

EDIT: Not a MapWithAI specific bug
​http://localhost:8111/features?q=add_node will also cause an NPE. It looks like we need to prepend a / if one doesn't exist.

[taylor.smock]

Prepend / to commands, if it doesn't exist

[taylor.smock]

Add non-regression test

[simon04]

In 16767/josm:

fix #19436 - RequestProcessor: do not add null objects to a JsonArray (patch by taylor.smock, modified)