The given key was not present in the dictionary solrnet - solr

Question

Please note: I know for the question SolrNet - The given key was not present in the dictionary and I have initialized solr object just like Mauricio suggests.
I am using solr 4.6.0 and solrnet build #173, .net framework 4.0 and VS2012 for development. For some unknown reason I am receiving error 'The given key was not present in the dictionary'. I have a document with that id in solr, I've checked via browser. It's a document like any other document. Why is error popping up? My code (I've made a comment on the place where the error happens):
//establishes connection with solr
private void ConnectToSolr()
{
try
{
if (_solr != null) return;
Startup.Init<Register>(SolrAddress);
_solr = ServiceLocator.Current.GetInstance<ISolrOperations<Register>>();
}
catch (Exception ex)
{
throw new Exception(ex.Message);
}
}
//Returns snippets from solr as BindingSource
public BindingSource GetSnippets(string searchTerm, DateTime? startDate = null, DateTime? endDate = null)
{
ConnectToSolr();
string dateQuery = startDate == null
? ""
: endDate == null
? "savedate:\"" + convertDateToSolrFormat(startDate) + "\"" //only start date
: "savedate:[" + convertDateToSolrFormat(startDate) + " TO " +
convertDateToSolrFormat(endDate) + "]";//range between start and end date
string textQuery = string.IsNullOrEmpty(searchTerm) ? "text:*" : "text:*" + searchTerm + "*";
List<Register> list = new List<Register>();
SolrQueryResults<Register> results;
string currentId = "";
try
{
results = _solr.Query(textQuery,
new QueryOptions
{
Highlight = new HighlightingParameters
{
Fields = new[] { "*" },
},
ExtraParams = new Dictionary<string, string>
{
{"fq", dateQuery},
{"sort", "savedate desc"}
}
});
for (int i = 0; i < results.Highlights.Count; i++)
{
currentId = results[i].Id;
var h = results.Highlights[currentId];
if (h.Snippets.Count > 0)
{
list.Add(new Register//here the error "the given key was not present in the dictionary pops up
{
Id = currentId,
ContentLiteral = h.Snippets["content"].ToArray()[0].Trim(new[]{' ', '\n'}),
SaveDateLiteral = results[i].SaveDate.ToShortDateString()
});
}
}
BindingList<Register> bindingList = new BindingList<Register>(list);
BindingSource bindingSource = new BindingSource();
bindingSource.DataSource = bindingList;
return bindingSource;
}
catch(Exception e)
{
MessageBox.Show(string.Format("{0}\nId:{1}", e.Message, currentId), "Solr error");
return null;
}
}

Answer 1

I've found out what's causing the problem: saving empty documents into solr. If I make an empty query (with text:*) through solrnet (usually I do this if I want to see all saved documents) and empty document is one of saved docs, then 'The given key is not present in dictionary pops up'. If all of the documents have text in them, this error doesn't pop up.

Answer 2

If you document contains fields with types other than string and you index null value to a double or integer field you will get the same error.
solr query return the null field as:
<null name="fieldname"/>
should be
<double name="fieldname">0.0</double>
or
<double name="fieldname"/>