Overly brittle to bad data

[foobacca]

I've regularly had sunburnt tripping over bad data and just flipping out. I added a little info to help debugging with this patch.

I'm wondering if it might be worth having a "non-strict" mode where it just makes the field value null rather than throwing an exception. This would suit my use case fine. It could be set as an argument to the constructor for SolrInterface, or maybe just on a per-query basis.

An example of the data I trip up on is:

I could have a go at writing this myself, but thought I'd just check if you'd be up for a "non-strict" mode.

[foobacca]

Oops, github didn't like the pre tag, lets try again with the bad data.

<arr name="publisher_id">
<int/>
</arr>