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https://issues.apache.org/jira/browse/CONFIGURATION-831?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17725817#comment-17725817
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Wojtek commented on CONFIGURATION-831:
--------------------------------------
Maybe it's just my impression and probably "should return empty string" would
be better. My train of though, let's assume this config:
```xml
<configuration>
<empty></empty>
<env>${env:VARIABLE}</env>
</configuration>
```
a) config.getString("empty") -> will `yield` empty string (`""`)
b) config.getString("nosuchproperty") -> will yield `null`
Now, for the "env":
1. if we have `VARIABLE="bla"`, config.getString("env") will yield "bla" (as
expected)
2. if we have variable set but without value (`VARIABLE=`),
config.getString("env") will yield empty string (`""`) (somewhat as expected I
guess)
3. if we don't have variable set, config.getString("env") will yield
`"${env:VARIABLE}"`.
In the last case `${env:VARIABLE}` would evaluate to null/"", and then
considering (a), my impression/expectation would be it should yield empty
string as well.
> Unresolved (non-existend) environment variables should return null
> ------------------------------------------------------------------
>
> Key: CONFIGURATION-831
> URL: https://issues.apache.org/jira/browse/CONFIGURATION-831
> Project: Commons Configuration
> Issue Type: New Feature
> Components: Interpolation
> Affects Versions: 2.9.0
> Reporter: Wojtek
> Priority: Minor
>
> Currently Interpolation of environment variables
> (https://commons.apache.org/proper/commons-configuration/userguide/howto_basicfeatures.html#Variable_Interpolation)
> return un-interpolated string if the environment variable doesn't exists at
> all.
> It would be very convenient and (I feel) more consistent if, in that case,
> 'null' would be returned.
>
> Alternatively, option to specify default if the variable doesn't exist would
> also work.
> I.e. something along the lines:
> ```
> ${env:JAVA_HOME:<default value>}
> ```
>
> From my experiments, even if we try to register custom interpolator it's not
> possible to explicitly return `null` from it.
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