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.

A variable that declares a type with @as is a different case and is not flagged from XSLT 2.0 on: <xsl:variable name="acc" as="node()*"/> binds the empty sequence of that type on purpose — a deliberate empty accumulator, not an accidental empty string. The exclusion is version-scoped: in XSLT 1.0 @as is not a recognized attribute, so it is inert and the variable still binds the empty string. A 1.0 stylesheet with an empty @as variable is therefore still flagged — the @as does not do what its author expects.

Incorrect:

<xsl:variable name="greeting"/>

Correct:

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

or:

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

Also correct — a typed empty sequence in XSLT 2.0 or 3.0:

<xsl:variable name="acc" as="node()*"/>