Bugfix for RdfMacroPipe

Empty name parameter in literal(..)-method resulted in an
StringIndexOutOfBoundsException. The parameter is checked with
org.apache.commons.lang.StringUtils now and so the use of empty name
parameter is possible again.
Merge pull request #150 from thaidlas/RdfMacroPipe-Bugfix

Bugfix for RdfMacroPipe