[JEXL-327] map[null] does not work in assignment context

• Type: Bug
• Status: Closed
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: 3.1
• Fix Version/s: 3.2
• Assignee: Unassigned
• Reporter: David Costanzo
• Created: 28/Jan/20 20:29
• Updated: 07/Jun/21 13:14
• Resolved: 29/Jan/20 16:59

Description

In JEXL, you can create a map with a null key by using a map literal and you can get the value associated with a null key.  However,  you can't assign a value to a null key, as in 

map[null] = 'bar'

This asymmetry is weird and might be an oversight.

 

Impact:

This has not blocked us from doing anything, so the impact nearly zero.  It's something I found while writing unit tests for my application, but it does not impact my users.  I'm mostly reporting it as a "language weirdness", in case the JEXL developers care.

That said, we do use null keys in maps.  In my domain (working with data from clinical trials), a null numeric value means "missing", which is a valid value.  Our JEXL programmers implement "switch" statements using a map, so you might see an expression that translates a coded variable named "DMSEX" into an English description like:

{
   null : "Unknown",
   1    : "MALE",
   2    : "FEMALE"
}[DMSEX]

Fortunately, this works as expected.  This bug only prevents us from building the lookup map programmatically, but we prefer using a literal, anyway.

 

Steps to Reproduce:

@Test
public void testSetNullKey() throws IOException {
    JexlEngine jexl = new JexlBuilder().create();
    JexlContext jc = new MapContext();
    JexlExpression expression1 = jexl.createExpression(
        "(function () {\n" +
        "  var map = {null : 'foo'};\n" +
        "  map[null] = 'bar';\n" +
        "  return map[null];\n" +
        "})()");

    // JEXL 3.1, throws JexlException$Property "unsolvable property '<?>.<null>'"
    // JEXL 3.2, throws JexlException$Property "undefined property '<?>.<null>'"
    Object o1 = expression1.evaluate(jc);
    Assert.assertEquals("bar", o1);
}

What Happens:

JEXL throws a JexlException.Property exception when it tries to evaluate "map[null] = 'bar'".

Expected Result:

"map[null] = 'bar'" changes the null key's value from "foo" to "bar" and the function returns "bar".