integrityCheck is not accepting String Provider, only String Literal

[DavidUnderdown]

integrityCheck has always been a little problematic on digitisation projects as we hadn't asked providers to include a line for the content folder itself in the tech_acq.csv. Lookign at the EBNF I thought I ought to be able to get around this by giving the subfolder parameter as $piece as the spec says it should accept a string provider (which covers string literals, column references and the other functions such as concat). However it seems that it will actually only accept a string literal.