RSolr::Error::InvalidRubyResponse when reindexing

[23tux]

Hi,

I found your gem and was very excited about it.
But I have a problem to get it running:

I started the solr server with rake sunspot:solr:run and then try to reindex my products with rake sunspot:reindex. After that, I get this error:

*Note: the reindex task will remove your current indexes and start from scratch.
If you have a large dataset, reindexing can take a very long time, possibly weeks.
This is not encouraged if you have anywhere near or over 1 million rows.
Are you sure you want to drop your indexes and completely reindex? (y/n)
y
Skipping progress bar: for progress reporting, add gem 'progress_bar' to your Gemfile
RSolr::Error::InvalidRubyResponse - 200 OK
Error: <result status="1">java.lang.NullPointerException
    at org.apache.solr.handler.XmlUpdateRequestHandler.doLegacyUpdate(XmlUpdateRequestHandler.java:129)
    at org.apache.solr.servlet.SolrUpdateServlet.doPost(SolrUpdateServlet.java:87)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1221)
    at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:297)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1212)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:399)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)

Request Data: "<?xml version=\"1.0\" encoding=\"UTF-8\"?><delete><query>type:Spree\\:\\:Product</query></delete>"

Backtrace: /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rsolr-1.0.9/lib/rsolr/client.rb:297:in `rescue in evaluate_ruby_response'
/usr/local/rvm/gems/ruby-1.9.3-p392/gems/rsolr-1.0.9/lib/rsolr/client.rb:294:in `evaluate_ruby_response'
/usr/local/rvm/gems/ruby-1.9.3-p392/gems/rsolr-1.0.9/lib/rsolr/client.rb:269:in `adapt_response'
/usr/local/rvm/gems/ruby-1.9.3-p392/gems/rsolr-1.0.9/lib/rsolr/client.rb:175:in `execute'
/usr/local/rvm/gems/ruby-1.9.3-p392/gems/rsolr-1.0.9/lib/rsolr/client.rb:161:in `send_and_receive'
(eval):2:in `post'
/usr/local/rvm/gems/ruby-1.9.3-p392/gems/rsolr-1.0.9/lib/rsolr/client.rb:67:in `update'
/usr/local/rvm/gems/ruby-1.9.3-p392/gems/rsolr-1.0.9/lib/rsolr/client.rb:131:in `delete_by_query'
/usr/local/rvm/gems/ruby-1.9.3-p392/gems/sunspot-2.0.0/lib/sunspot/indexer.rb:57:in `remove_all'
/usr/local/rvm/gems/ruby-1.9.3-p392/gems/sunspot-2.0.0/lib/sunspot/session.rb:181:in `block in remove_all'
/usr/local/rvm/gems/ruby-1.9.3-p392/gems/sunspot-2.0.0/lib/sunspot/session.rb:181:in `each'

I just started using Solr, so I'm a little bit lost here. Can someone help me or point me in the right direction where I can start?