[jira] Commented: (TAPESTRY-1978) When passing in empty parameter, indicate problem parameter in error message.

["Kevin Menard (JIRA)" <de...@tapestry.apache.org>]

    [ https://issues.apache.org/jira/browse/TAPESTRY-1978?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12569348#action_12569348 ] 

Kevin Menard commented on TAPESTRY-1978:
----------------------------------------

I've just delved into the issue a bit more.  The source of the problem is:

BindingSourceImpl:50
notBlank(expression, "expression");

While the error message is technically accurate, it lacks any context to help the user figure out what's wrong.

The description value supplied includes the source parameter that is in error, but it is appended to the string "parameter " in PageElementFactoryImpl:305.  A hackish way of dealing with this is to do a substring to extract what we want.  That's highly caller dependent, however.  What we really should do is pass the parameter name as a separate parameter, which would necessitate either an interface change or addition.

It should be noted that the location value would help immensely as well, although it only shows the component in error, not the parameter value.  Due to the fail fast nature of notBlank, the location value is essentially discarded.  So, that should be wrapped up nicely as well.

> When passing in empty parameter, indicate problem parameter in error message.
> -----------------------------------------------------------------------------
>
>                 Key: TAPESTRY-1978
>                 URL: https://issues.apache.org/jira/browse/TAPESTRY-1978
>             Project: Tapestry
>          Issue Type: Improvement
>          Components: Framework
>    Affects Versions: 5.0.7
>            Reporter: Kevin Menard
>            Priority: Minor
>
> While prototyping a page recently, I decided to hold off on passing in parameters until I had a good sense of what their names should be.  So, I had something similar to:
> <t:textfield value=""/>
> Clearly this is a broken construct and Tapestry generally recognized it.  I was greeted with the following error message:
> "Parameter expression was null or contained only whitespace."
> And a highlighted block of my template.  Unfortunately, the highlighted block is not where the problem was.  Likewise, the error message really didn't indicate what parameter was broken of what component.  After a little bit of guess-and-check, I caught the obvious error.  It'd be nice if Tapestry handled this for me though.

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