Index hardcoded in SolrField Derivative

[duartegarin]

The Solr index is hardcoded in the derivative so crashes this module on install, unless you change it to an existing index.

[joaogarin]

I quick fixed it. I still want to make this better so that one can only select fields from the right index..but I am finding it hard to make this work. for now it just autosuggests all fields from any index :/ not great. some room for improvement. fixed in 7dd2f4d