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https://issues.apache.org/jira/browse/JXPATH-151?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13046117#comment-13046117
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Matt Benson commented on JXPATH-151:
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Setting up a similar map to what you have described, and accessing via a bean
property I still found the errors you describe. This issue was fairly
difficult to triage, but my final diagnosis is that it is indicative of a bug.
It is interesting to note that the {{value[@name='a'] != value[@name='b]}}
approach succeeded, although I would still consider it dangerous to depend on
{{null}} values in JXPath. For example, if you add a mapping of {{"d":0}} to
your map, you will find that {{value[@name='d'] = value[@name='b']}} because
the fact that {{d}} refers to a numeric type forces the conversion of {{b}}'s
{{null}} value to a number, {{0.0}}. XPath is tricky this way, and JXPath,
dealing with types unknown to the XPath specification only becomes trickier.
Having said all that, and to return to the issue at hand, I found that certain
existing JXPath tests assert that it should be possible to get a {{null}} value
from the expression {{bean.nullProperty}}, but that iterating pointers from the
expression {{bean.nullProperty[1]}} should yield no results. But this assigns
a Java-centric meaning to XPath's {{[1]}} test, and it is my judgment that this
is overstepping given that Javadoc for relevant methods states that
non-Collection items should be treated as having length 1. Making the
conscious decision to _change_ an existing unit test is not a decision to make
lightly, but in this case my opinion is that it is warranted.
> null handling is inconsistent
> -----------------------------
>
> Key: JXPATH-151
> URL: https://issues.apache.org/jira/browse/JXPATH-151
> Project: Commons JXPath
> Issue Type: Bug
> Affects Versions: 1.3
> Environment: windows oracle jvm 1.6_25
> Reporter: Johannes Stelzer
> Priority: Blocker
>
> Comparing a vaule to null using unequals (\!=) yields false!
> {noformat}
> Map<String, Integer> m = new HashMap<String, Integer>();
> m.put("a", 1);
> m.put("b", null);
> m.put("c", 1);
> JXPathContext c = JXPathContext.newContext(m);
> System.out.println(c.getValue("a != b") + " should be true");
> System.out.println(c.getValue("a != c") + " should be false");
> System.out.println(c.getValue("a = b") + " should be false");
> System.out.println(c.getValue("a = c") + " should be true");
> System.out.println(c.getValue("not(a = b)") + " should be true");
> System.out.println(c.getValue("not(a = c)") + " should be false");
> {noformat}
> Output using 1.3:
> {color:red} false should be true{color}
> false should be false
> false should be false
> true should be true
> true should be true
> false should be false
> In 1.2 it works correctly!
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