ClassCastException during template compilation (Variable cannot be cast to Param)

A DESCRIPTION OF THE PROBLEM :
When compiling xslt template ClassCastException is thrown, which is unexpected. Example code below. If template is invalid TransformerConfigurationException should be thrown.
Problem is in SymbolTable.java

   public Param addParam(Param parameter) {
        if (_variables == null) _variables = new HashMap<>();
        final String name = parameter.getName().getStringRep();
        return (Param)_variables.put(name, parameter);
    }

_variables can contain Param and Variable objects, so this cast causes ClassCastException



STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the example code

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No exception should be thrown.
ACTUAL -
java.lang.ClassCastException: class com.sun.org.apache.xalan.internal.xsltc.compiler.Variable cannot be cast to class com.sun.org.apache.xalan.internal.xsltc.compiler.Param (com.sun.org.apache.xalan.internal.xsltc.compiler.Variable and com.sun.org.apache.xalan.internal.xsltc.compiler.Param are in module java.xml of loader 'bootstrap')
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.SymbolTable.addParam(SymbolTable.java:104)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Param.parseContents(Param.java:137)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Stylesheet.parseOwnChildren(Stylesheet.java:587)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Stylesheet.parseContents(Stylesheet.java:559)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Parser.createAST(Parser.java:398)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.XSLTC.compile(XSLTC.java:493)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.XSLTC.compile(XSLTC.java:570)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl.newTemplates(TransformerFactoryImpl.java:1018)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl.newTransformer(TransformerFactoryImpl.java:817)
at Scratch.main(scratch_1.java:23)
ERROR: 'Could not compile stylesheet'
FATAL ERROR: 'class com.sun.org.apache.xalan.internal.xsltc.compiler.Variable cannot be cast to class com.sun.org.apache.xalan.internal.xsltc.compiler.Param (com.sun.org.apache.xalan.internal.xsltc.compiler.Variable and com.sun.org.apache.xalan.internal.xsltc.compiler.Param are in module java.xml of loader 'bootstrap')'
           :class com.sun.org.apache.xalan.internal.xsltc.compiler.Variable cannot be cast to class com.sun.org.apache.xalan.internal.xsltc.compiler.Param (com.sun.org.apache.xalan.internal.xsltc.compiler.Variable and com.sun.org.apache.xalan.internal.xsltc.compiler.Param are in module java.xml of loader 'bootstrap')
Exception in thread "main" javax.xml.transform.TransformerConfigurationException: class com.sun.org.apache.xalan.internal.xsltc.compiler.Variable cannot be cast to class com.sun.org.apache.xalan.internal.xsltc.compiler.Param (com.sun.org.apache.xalan.internal.xsltc.compiler.Variable and com.sun.org.apache.xalan.internal.xsltc.compiler.Param are in module java.xml of loader 'bootstrap')
at java.xml/com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl.newTemplates(TransformerFactoryImpl.java:1059)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl.newTransformer(TransformerFactoryImpl.java:817)
at Scratch.main(scratch_1.java:23)
Caused by: java.lang.ClassCastException: class com.sun.org.apache.xalan.internal.xsltc.compiler.Variable cannot be cast to class com.sun.org.apache.xalan.internal.xsltc.compiler.Param (com.sun.org.apache.xalan.internal.xsltc.compiler.Variable and com.sun.org.apache.xalan.internal.xsltc.compiler.Param are in module java.xml of loader 'bootstrap')
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.SymbolTable.addParam(SymbolTable.java:104)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Param.parseContents(Param.java:137)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Stylesheet.parseOwnChildren(Stylesheet.java:587)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Stylesheet.parseContents(Stylesheet.java:559)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Parser.createAST(Parser.java:398)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.XSLTC.compile(XSLTC.java:493)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.XSLTC.compile(XSLTC.java:570)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl.newTemplates(TransformerFactoryImpl.java:1018)
... 2 more
---------
java.lang.ClassCastException: class com.sun.org.apache.xalan.internal.xsltc.compiler.Variable cannot be cast to class com.sun.org.apache.xalan.internal.xsltc.compiler.Param (com.sun.org.apache.xalan.internal.xsltc.compiler.Variable and com.sun.org.apache.xalan.internal.xsltc.compiler.Param are in module java.xml of loader 'bootstrap')
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.SymbolTable.addParam(SymbolTable.java:104)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Param.parseContents(Param.java:137)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Stylesheet.parseOwnChildren(Stylesheet.java:587)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Stylesheet.parseContents(Stylesheet.java:559)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.Parser.createAST(Parser.java:398)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.XSLTC.compile(XSLTC.java:493)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.compiler.XSLTC.compile(XSLTC.java:570)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl.newTemplates(TransformerFactoryImpl.java:1018)
at java.xml/com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl.newTransformer(TransformerFactoryImpl.java:817)
at Scratch.main(scratch_1.java:23)


---------- BEGIN SOURCE ----------

import javax.xml.transform.TransformerFactory;
import javax.xml.transform.stream.StreamSource;
import java.io.StringReader;

class Scratch {

    public static void main(String[] args) throws Exception {
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        String stylesheet = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
                "<xsl:stylesheet xmlns:xsl=\"http://www.w3.org/1999/XSL/Transform\" version=\"1.0\">\n" +
                " <xsl:variable name=\"background-color\">#f4f4f4</xsl:variable>\n" +
                " <xsl:param name=\"background-color\">pp</xsl:param>\n" +
                " <xsl:template name=\"tName\"><xsl:param name=\"background-color\">black</xsl:param>\n" +
                " OK <xsl:value-of select=\"$background-color\"/>\n" +
                " </xsl:template>\n" +
                " <xsl:template match=\"/root\">\n" +
                " <xsl:call-template name=\"tName\">\n" +
                " <xsl:with-param name=\"background-color\" select=\"$background-color\"/>\n" +
                " </xsl:call-template>\n" +
                " </xsl:template>\n" +
                "</xsl:stylesheet>\n";
        transformerFactory.newTransformer(new StreamSource(new StringReader(stylesheet)));

    }
}
---------- END SOURCE ----------

FREQUENCY : always