Empty xsl:variable

An xsl:variable gets its value either from a @select attribute or from the sequence constructor inside it. With neither, the variable binds to an empty string — almost always a mistake, and at best a confusing way to declare an empty value. State the value explicitly or drop the declaration.

Incorrect:

<xsl:variable name="greeting"/>

Correct:

<xsl:variable name="greeting" select="'hello'"/>

or:

<xsl:variable name="greeting">hello</xsl:variable>