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https://issues.apache.org/jira/browse/HADOOP-6948?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12908939#action_12908939
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Doug Cutting commented on HADOOP-6948:
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> If you want to run jobs with configurations created on the fly (which is what 
> I'm doing) then the inability to remove properties is kind of annoying.

I don't yet fully understand the need.  I've written lots of code that creates 
configurations and have never wanted to remove a property.  That said, I don't 
find it inconceivable that there might be reasonable cases.  Can you perhaps 
humor me and elaborate a bit more how it comes that you have properties that 
you need to erase?  Changing a datastructure from write-only to read-write 
means that applications can less safely cache values from it.  But since 
Configuration is already permits overwrites this is perhaps a non-issue.

Also, do you intend to provide a patch for this?  My instinct is that, if we 
were to provide the ability to remove Configuration properties, it should be 
done through a 'remove' method rather than by setting values to null.  Do you 
agree?

> There's no way to remove a property from a Configuration
> --------------------------------------------------------
>
>                 Key: HADOOP-6948
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6948
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: conf
>    Affects Versions: 0.20.2, 0.21.0
>         Environment: all
>            Reporter: Mike Baranczak
>            Priority: Minor
>
> The Configuration class has a lot of methods for setting properties, but it's 
> impossible to remove a property once it's set. Trying to set it to null 
> results in a NullPointerException, since java.util.Properties doesn't allow 
> null values. When building a Configuration programmatically, this can be a 
> problem. 

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