data import fails to 5.3.0: investigate

there are two errors we encounter at import since we updated to 5.3.0.

tei2html:find-referenced-node-id(element(), xs:string) xs:string?. Expected cardinality: zero or one, got 2.

existdb_1           | (Line: 61 /db/apps/ahikar/modules/AnnotationAPI/save-annotations.xqm) Recreate annotation items for TEI file 3r672
existdb_1           | (Line: 78 /db/apps/ahikar/modules/AnnotationAPI/save-annotations.xqm) Storing finished. For possible errors in this process see exist.log.
existdb_1           | 06 Jul 2021 07:10:48,951 [qtp1280452839-36] INFO  (LogFunction.java [writeLog]:205) - (Line: 21 /db/apps/ahikar/modules/save-html.xqm) Recreate HTML files for TEI file 3r672 
existdb_1           | 06 Jul 2021 07:10:48,997 [qtp1280452839-36] INFO  (LogFunction.java [writeLog]:205) - (Line: 32 /db/apps/ahikar/modules/save-html.xqm) Stored HTML files for TEI file 3r672, page 90v 
existdb_1           | 06 Jul 2021 07:10:49,017 [qtp1280452839-36] ERROR (DeferredFunctionCall.java [isEmpty]:204) - Exception in deferred function: exerr:ERROR The actual return type does not match the sequence type declared in the function's signature: tei2html:find-referenced-node-id(element(), xs:string) xs:string?. Expected cardinality: zero or one, got 2. [at line 208, column 50, source: /db/apps/ahikar/modules/tei2html.xqm]
existdb_1           | In function:
existdb_1           | 	tei2html:find-referenced-node-id(element(), xs:string) [203:27:/db/apps/ahikar/modules/tei2html.xqm]
existdb_1           | 	tei2html:get-href-value(element()) [184:25:/db/apps/ahikar/modules/tei2html.xqm]
existdb_1           | 	tei2html:make-xhtml-a(element()) [106:58:/db/apps/ahikar/modules/tei2html.xqm]
existdb_1           | 	tei2html:make-default-return(node()*) [80:13:/db/apps/ahikar/modules/tei2html.xqm]
existdb_1           | 	tei2html:transform(node()*) [75:21:/db/apps/ahikar/modules/tei2html.xqm] 
existdb_1           | 06 Jul 2021 07:10:49,018 [qtp1280452839-36] ERROR (DeferredFunctionCall.java [isEmpty]:204) - Exception in deferred function: exerr:ERROR The actual return type does not match the sequence type declared in the function's signature: tei2html:find-referenced-node-id(element(), xs:string) xs:string?. Expected cardinality: zero or one, got 2. [at line 208, column 50, source: /db/apps/ahikar/modules/tei2html.xqm]

err:FORX0003 regular expression could match empty string

ERROR (DeferredFunctionCall.java [isEmpty]:204) - Exception in deferred function: err:FORX0003 regular expression could match empty string [at line 1071, column 22, source: /exist/etc/../data/expathrepo/functx-1.0.1/functx/functx.xq]
In function:
	functx:index-of-match-first(xs:string?, xs:string) [898:17:/exist/etc/../data/expathrepo/functx-1.0.1/functx/functx.xq]
	functx:get-matches-and-non-matches(xs:string?, xs:string) [126:20:/exist/etc/../data/expathrepo/functx-1.0.1/functx/functx.xq]
	tei2html-text:get-text-unaffected-by-word-break(text(), xs:string) [200:24:/db/apps/ahikar/modules/tei2html-textprocessing.xqm]
	tei2html-text:make-lb-combi-at-line-beginning(text()) [35:69:/db/apps/ahikar/modules/tei2html-textprocessing.xqm]
	tei2html-text:process-text(text()) [37:13:/db/apps/ahikar/modules/tei2html-textprocessing.xqm]
	tei2html:transform(node()*) [146:9:/db/apps/ahikar/modules/tei2html.xqm] 
06 Jul 2021 08:30:26,876 [qtp1793469566-41] ERROR (DeferredFunctionCall.java [isEmpty]:204) - Exception in deferred function: err:FORX0003 regular expression could match empty string [at line 1071, column 22, source: /exist/etc/../data/expathrepo/functx-1.0.1/functx/functx.xq]