@yegor256 this PR closes #105 by adding the missing regression test for the empty <xsl:stylesheet> case from the issue.

What was missing

XSLDocumentTest had no coverage for the empty-stylesheet input shown in the issue body:

<xsl:stylesheet xmlns:xsl='http://www.w3.org/1999/XSL/Transform' version='2.0'></xsl:stylesheet>

What this adds

A new test emptyStylesheetExtractsTextContent that:

1. Constructs an XSLDocument from the empty stylesheet from the issue.
2. Calls applyTo(...) on <a><b>hello</b><c>world</c></a>.
3. Asserts the output contains helloworld, which is the documented XSLT behavior: with no template rules defined, the built-in templates traverse the tree and emit text nodes verbatim, so the concatenated text content is the expected result.

This pins the documented XSLT default-rules behavior so future regressions in XSLDocument (e.g. accidentally rejecting an empty stylesheet at construction time, or breaking text extraction) will be caught.

Verification

• mvn -B clean install -Pqulice passes locally on Java 21.
• All 14 CI checks are green on this PR.