Error in DIH after upgrading from 4.0 to 4.1

[Boris Granveaud]

Hello,

I've just tried to upgrade from 4.0 to 4.1 and I have the following
exception when reindexing my data:

Caused by: java.lang.UnsupportedOperationException
 at java.util.Collections$UnmodifiableMap.put(Collections.java:1283)
at
org.apache.solr.handler.dataimport.VariableResolver.currentLevelMap(VariableResolver.java:204)
 at
org.apache.solr.handler.dataimport.VariableResolver.resolve(VariableResolver.java:94)
at
org.apache.solr.handler.dataimport.VariableResolver.replaceTokens(VariableResolver.java:144)
 at
org.apache.solr.handler.dataimport.ContextImpl.replaceTokens(ContextImpl.java:254)
at
org.apache.solr.handler.dataimport.JdbcDataSource.resolveVariables(JdbcDataSource.java:203)
 at
org.apache.solr.handler.dataimport.JdbcDataSource.createConnectionFactory(JdbcDataSource.java:101)
at
org.apache.solr.handler.dataimport.JdbcDataSource.init(JdbcDataSource.java:62)
 at
org.apache.solr.handler.dataimport.DataImporter.getDataSourceInstance(DataImporter.java:394)

It seems to be related to the use of placeholders in data-config.xml:

<dataConfig>
    <dataSource type="JdbcDataSource"
                name="bceDS"
                driver="${dataimporter.request.solr.bceDS.driver}"
                url="${dataimporter.request.solr.bceDS.url}"
                user="${dataimporter.request.solr.bceDS.user}"
                password="${dataimporter.request.solr.bceDS.password}"
                batchSize="-1"/>

solrconfig.xml:

<requestHandler name="/dataimport"
class="org.apache.solr.handler.dataimport.DataImportHandler">
 <lst name="defaults">
<str name="config">data-config.xml</str>

<!-- dataSource parameters for data-config.xml -->
<str name="solr.bceDS.driver">...</str>
 <str name="solr.bceDS.url">...</str>
<str name="solr.bceDS.user">...</str>
 <str name="solr.bceDS.password">...</str>
</lst>
</requestHandler>

Did I miss something or is it a bug?

Thanks,
Boris.