Add test case that references an excluded empty matcher group

Author: fsteeg

src/test/java/org/culturegraph/mf/morph/functions/Regexp.xml

@@ -20,6 +20,9 @@
 					<mm:data source="001." name="subject">
 						<mm:regexp match=".*" format="resource:P${0}" />
 					</mm:data>
+					<mm:data source="001." name="subject">
+						<mm:regexp match=".*" format="${1}"/>
+					</mm:data>
 					<mm:data source="001." name="subject">
 						<mm:regexp match=".*" />
 					</mm:data>
@@ -31,6 +34,7 @@
 				<cgxml:records>
 					<cgxml:record id="1">
 						<cgxml:literal name="subject" value="resource:P184000" />
+						<cgxml:literal name="subject" value="" />
 						<cgxml:literal name="subject" value="184000" />
 					</cgxml:record>
 				</cgxml:records>