return type error in index-api

2019-12-30 14:33:15,216 [qtp1432888450-6352] ERROR (RestXqServlet.java [service]:108) - exerr:ERROR The actual return type does not match the sequence type declared in the function's signature: index:search(xs:string, item()*) array(*). Expected cardinality: exactly one, got 0. [at line 265, column 22, source: /db/apps/SADE/modules/fontane/index-api.xqm]
In function:
        index:search(xs:string, item()*) [-1:-1:/db/apps/SADE/modules/fontane/index-api.xqm] 
org.exquery.restxq.RestXqServiceException: exerr:ERROR The actual return type does not match the sequence type declared in the function's signature: index:search(xs:string, item()*) array(*). Expected cardinality: exactly one, got 0. [at line 265, column 22, source: /db/apps/SADE/modules/fontane/index-api.xqm]
In function:
        index:search(xs:string, item()*) [-1:-1:/db/apps/SADE/modules/fontane/index-api.xqm]
        at org.exist.extensions.exquery.restxq.impl.ResourceFunctionExecutorImpl.execute(ResourceFunctionExecutorImpl.java:197) ~[exist-restxq-4.7.0.jar:4.7.0]
        at org.exquery.restxq.impl.AbstractRestXqService.service(AbstractRestXqService.java:192) ~[exquery-restxq-0.1.34.jar:0.1.34]
        at org.exist.extensions.exquery.restxq.impl.RestXqServiceImpl.service(RestXqServiceImpl.java:124) ~[exist-restxq-4.7.0.jar:4.7.0]
        at org.exist.extensions.exquery.restxq.impl.RestXqServlet.service(RestXqServlet.java:87) [exist-restxq-4.7.0.jar:4.7.0]
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) [servlet-api-3.1.jar:3.1.0]
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