Metadata Import via Scopus API: improved handling of empty search results

[saschaszott]

Bug Description

An empty search result which is returned from the Elsevier Scopus REST API looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<search-results xmlns="http://www.w3.org/2005/Atom" xmlns:dc="http://purl.org/dc/elements/1.1/"
                xmlns:opensearch="http://a9.com/-/spec/opensearch/1.1/"
                xmlns:prism="http://prismstandard.org/namespaces/basic/2.0/" xmlns:atom="http://www.w3.org/2005/Atom">
    <opensearch:totalResults>0</opensearch:totalResults>
    <opensearch:startIndex>0</opensearch:startIndex>
    <opensearch:itemsPerPage>0</opensearch:itemsPerPage>
    <opensearch:Query role="request" searchTerms="a-query-without-hits" startPage="0"/>
    <link ref="self"
          href="https://api.elsevier.com/content/search/scopus?start=0&amp;count=10&amp;query=a-query-without-hits&amp;httpAccept=application%2Fxml"
          type="application/xml"/>
    <entry>
        <error>Result set was empty</error>
    </entry>
</search-results>

The implementation in ScopusImportMetadataSourceServiceImpl considers this kind of result as a not-empty result.

In consequence, this leads to this unexpected state in the UI:

[saschaszott]

In DS-CRIS 7, the test class ScopusImportMetadataSourceServiceIT was extended: it contains a test (scopusImportMetadataGetRecordsEmptyResponseTest) which covers an empty search result. Is it ok to merge the changes in ScopusImportMetadataSourceServiceIT which were added by 4Science in the DS CRIS repo? In this case, the test case scopusImportMetadataGetRecordsEmptyResponseTest has to be adapted in this way: https://github.com/4Science/DSpace/pull/434/files#diff-12daf99ec2c1ccf4239c0b7fa4d21a2b0b81eb37ba36d1bfbbe79396d7658808

[tdonohue]

@saschaszott : My understanding from the 4Science team (pinging @abollini ) is that they welcome code being ported from DSpace-CRIS back to DSpace. So, I think it's safe to port that test back to DSpace....provided it can be easily ported & works just as well on DSpace.

[saschaszott]

@tdonohue , @abollini : I've merged the changes which were applied to ScopusImportMetadataSourceServiceImpl in DSC7 into this PR

[tdonohue]

@saschaszott : Looking at the IT failures in this PR, it appears it may be failing its own tests?