Expression map min-count

[chrdebru]

The SHACL shape of an expression map contains, on line 45, a min-count that is 1. We discussed the need for the generation of blank nodes based on the iteration, which is important for RML-CC as we want to generate lists and containers without explicit book-keeping of their members. We discussed that this could also be useful for generating blank nodes "on the fly."

[dachafra]

@chrdebru this is a duplicated issue, #210 was open and indeed, the solution has been already proposed and it's waiting for your approval ;-) #238