Use choose without otherwise

An xsl:choose with two or more xsl:when branches but no xsl:otherwise silently produces no output when none of them matches. Add xsl:otherwise to handle unexpected values explicitly. (A single-when choose is better written as an xsl:if — use-single-option-for-choose — and one with no xsl:when at all is reported by empty-choose.)

Incorrect:

<xsl:choose>
  <xsl:when test="@type = 'a'">A</xsl:when>
  <xsl:when test="@type = 'b'">B</xsl:when>
</xsl:choose>

Correct:

<xsl:choose>
  <xsl:when test="@type = 'a'">A</xsl:when>
  <xsl:when test="@type = 'b'">B</xsl:when>
  <xsl:otherwise>Unknown</xsl:otherwise>
</xsl:choose>