[jira] [Created] (JEXL-387) v3.2.1 breaks with log-related NullPointerException

["Garret Wilson (Jira)" <ji...@apache.org>]

Garret Wilson created JEXL-387:
----------------------------------

             Summary: v3.2.1 breaks with log-related NullPointerException
                 Key: JEXL-387
                 URL: https://issues.apache.org/jira/browse/JEXL-387
             Project: Commons JEXL
          Issue Type: Bug
         Environment: Java 17; Windows 10
            Reporter: Garret Wilson


In my [Guise Mummy|https://github.com/globalmentor/guise-mummy] static site generator I'm using JEXL to interpret the built-in [Mesh Expression Language|https://github.com/globalmentor/guise-mummy/tree/main/mesh] (MEXL). Everything was working fine with JEXL 3.1. In fact the entire [Guise Mummy web site|https://guise.io/mummy/] itself was produced using Guise Mummy with MEXL on top of JEXL.

But when I upgrade to JEXL 3.2.1, the unit tests break. The MEX+JEXL error message says "Error in MEXL expression `foo.bar`: io.guise.mesh.JexlMexlEvaluator.evaluate:93 undefined property 'bar'", but if you look in the stack trace, you'll see that the problem seems to be a deeper {{NullPointerException}} which {{InterpreterBase.getAttribute(…)}} catches and effectively ignores, making it look like the problem was a missing variable.

{code:xml}
} catch (final Exception xany) {
  xcause = xany;
}
{code}

Here's the real problem:

{noformat}
Caused by: java.lang.NullPointerException: Cannot invoke "org.apache.commons.logging.Log.isDebugEnabled()" because "log" is null
	at org.apache.commons.jexl3.internal.introspection.ClassMap.populateWithClass(ClassMap.java:296)
	at org.apache.commons.jexl3.internal.introspection.ClassMap.populateWithInterface(ClassMap.java:270)
	at org.apache.commons.jexl3.internal.introspection.ClassMap.create(ClassMap.java:229)
	at org.apache.commons.jexl3.internal.introspection.ClassMap.<init>(ClassMap.java:100)
	at org.apache.commons.jexl3.internal.introspection.Introspector.getMap(Introspector.java:315)
	at org.apache.commons.jexl3.internal.introspection.Introspector.getMethod(Introspector.java:146)
	at org.apache.commons.jexl3.internal.introspection.Introspector.getMethod(Introspector.java:133)
	at org.apache.commons.jexl3.internal.introspection.PropertyGetExecutor.discoverGet(PropertyGetExecutor.java:107)
	at org.apache.commons.jexl3.internal.introspection.PropertyGetExecutor.discover(PropertyGetExecutor.java:42)
	at org.apache.commons.jexl3.internal.introspection.Uberspect.getPropertyGet(Uberspect.java:263)
	at org.apache.commons.jexl3.internal.InterpreterBase.getAttribute(InterpreterBase.java:971)
	at org.apache.commons.jexl3.internal.Interpreter.visit(Interpreter.java:1108)
	at org.apache.commons.jexl3.parser.ASTIdentifierAccess.jjtAccept(ASTIdentifierAccess.java:104)
	at org.apache.commons.jexl3.internal.Interpreter.visit(Interpreter.java:1156)
	at org.apache.commons.jexl3.parser.ASTReference.jjtAccept(ASTReference.java:19)
	at org.apache.commons.jexl3.internal.Interpreter.visit(Interpreter.java:1029)
	at org.apache.commons.jexl3.parser.ASTJexlScript.jjtAccept(ASTJexlScript.java:58)
	at org.apache.commons.jexl3.internal.Interpreter.interpret(Interpreter.java:193)
	at org.apache.commons.jexl3.internal.Script.execute(Script.java:188)
	at org.apache.commons.jexl3.internal.Script.evaluate(Script.java:180)
	... 72 more
{noformat}

For some reason your internal {{ClassMap}} class is being passed a {{Log}} that is {{null}}. Looking up the stack trace, it would appear this is coming from your {{Introspector}}. (There is a similar [error on Stack Overflowhttps://stackoverflow.com/q/64927054] with no answers; I don't know if they are using JAXL.)

* First, passing the {{Log}} around as a parameter is an antipattern. Logging is a cross-cutting concern; passing it around as a parameter is a bad idea.
* I wish you were using {{SLF4J}} like practically everyone else instead of {{org.apache.commons.logging}}.
* You shouldn't catch {{NullPointerException}} and turn it into a "normal" error condition, trying to say that a variable wasn't defined when really this was an internal error with the library.

In any case, for some reason JEXL 3.2.1 isn't initializing its internal logging support.

To reproduce this:

# Clone [Guise Mummy 0.5.3|https://github.com/globalmentor/guise-mummy/releases/tag/v0.5.3].
# In the overall project {{pom.xml}}, change the version of {{org.apache.commons:commons-jexl3}} from {{<version>3.1</version>}} to {{<version>3.2.1</version>}}.
# Run {{mvn clean verify}}.



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