Saxon

Some XQuery similar to this one was mistyped by omitting "or" before the quantified expression:

    declare function local:f($x, $y)
    {
      let $a := $x
      where empty($y)   (every $i in $x satisfies $i = $y)
      return $a
    };
    local:f("x", ())

The optimizer throws this exception:

    java.lang.NullPointerException
        at net.sf.saxon.expr.flwor.FLWORExpression.optimize(FLWORExpression.java:558)
        at net.sf.saxon.expr.parser.ExpressionVisitor.optimize(ExpressionVisitor.java:244)
        at net.sf.saxon.query.XQueryFunction.optimize(XQueryFunction.java:471)
        at net.sf.saxon.query.XQueryFunctionLibrary.optimizeGlobalFunctions(XQueryFunctionLibrary.java:326)
        at net.sf.saxon.query.QueryModule.optimizeGlobalFunctions(QueryModule.java:1208)
        at net.sf.saxon.expr.instruct.Executable.fixupQueryModules(Executable.java:597)
        at net.sf.saxon.query.XQueryParser.makeXQueryExpression(XQueryParser.java:159)
        at net.sf.saxon.query.StaticQueryContext.compileQuery(StaticQueryContext.java:571)
        at net.sf.saxon.query.StaticQueryContext.compileQuery(StaticQueryContext.java:634)
        at net.sf.saxon.s9api.XQueryCompiler.compile(XQueryCompiler.java:592)
        at net.sf.saxon.Query.compileQuery(Query.java:787)
        at net.sf.saxon.Query.doQuery(Query.java:340)
        at net.sf.saxon.Query.main(Query.java:111)

With the "or" in place, i.e.

    declare function local:f($x, $y)
    {
      let $a := $x
      where empty($y) or (every $i in $x satisfies $i = $y)
      return $a
    };
    local:f("x", ())

there is an exception, too:

    java.lang.ClassCastException: net.sf.saxon.expr.Literal cannot be cast to net.sf.saxon.expr.VariableReference
        at com.saxonica.ee.optim.IndexedLookupExpression.replaceOperand(IndexedLookupExpression.java:204)
        at net.sf.saxon.expr.parser.ExpressionTool.inlineVariableReferences(ExpressionTool.java:1300)
        at net.sf.saxon.expr.parser.ExpressionTool.inlineVariableReferences(ExpressionTool.java:1303)
        at net.sf.saxon.expr.Assignation.replaceVariable(Assignation.java:470)
        at net.sf.saxon.expr.LetExpression.optimize(LetExpression.java:231)
        at net.sf.saxon.expr.parser.ExpressionVisitor.optimize(ExpressionVisitor.java:244)
        at net.sf.saxon.expr.BinaryExpression.optimize(BinaryExpression.java:90)
        at net.sf.saxon.expr.BooleanExpression.optimize(BooleanExpression.java:105)
        at net.sf.saxon.expr.OrExpression.optimize(OrExpression.java:55)
        at net.sf.saxon.expr.parser.ExpressionVisitor.optimize(ExpressionVisitor.java:244)
        at net.sf.saxon.expr.flwor.FLWORExpression$7.processExpression(FLWORExpression.java:490)
        at net.sf.saxon.expr.flwor.WhereClause.processSubExpressions(WhereClause.java:111)
        at net.sf.saxon.expr.flwor.FLWORExpression.optimize(FLWORExpression.java:488)
        at net.sf.saxon.expr.parser.ExpressionVisitor.optimize(ExpressionVisitor.java:244)
        at net.sf.saxon.expr.LetExpression.optimize(LetExpression.java:198)
        at net.sf.saxon.expr.parser.ExpressionVisitor.optimize(ExpressionVisitor.java:244)
        at net.sf.saxon.expr.LetExpression.optimize(LetExpression.java:198)
        at net.sf.saxon.expr.parser.ExpressionVisitor.optimize(ExpressionVisitor.java:244)
        at com.saxonica.ee.optim.OptimizerEE.tryInlineFunctionCall(OptimizerEE.java:1053)
        at net.sf.saxon.expr.UserFunctionCall.optimize(UserFunctionCall.java:343)
        at net.sf.saxon.query.XQueryExpression.<init>(XQueryExpression.java:81)
        at com.saxonica.ee.optim.XQueryExpressionEE.<init>(XQueryExpressionEE.java:54)
        at com.saxonica.config.EnterpriseConfiguration.makeXQueryExpression(EnterpriseConfiguration.java:1526)
        at net.sf.saxon.query.XQueryParser.makeXQueryExpression(XQueryParser.java:173)
        at net.sf.saxon.query.StaticQueryContext.compileQuery(StaticQueryContext.java:571)
        at net.sf.saxon.query.StaticQueryContext.compileQuery(StaticQueryContext.java:634)
        at net.sf.saxon.s9api.XQueryCompiler.compile(XQueryCompiler.java:592)
        at net.sf.saxon.Query.compileQuery(Query.java:787)
        at net.sf.saxon.Query.doQuery(Query.java:340)
        at net.sf.saxon.Query.main(Query.java:111)

Tested from command line using Saxon-EE 9.6.0.7J.