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Retrieving values form Salesforce Activity History

I am trying to retrieve values from the SalesForce Activity History.  The Activity History itself is not directly queryable but can be accessed in a subquery.  The following SOQL query works just fine in SF:
SELECT Id, (SELECT Subject FROM ActivityHistories) FROM Lead LIMIT 5
When I run this query in Talend however I get this...
|Id                |Lead_ActivityHistories_Subject|
|00Q6000000IAUwSEAX|null                          |
|00Q6000000IYWMWEA5|null                          |
|00Q6000000IYwlEEAT|null                          |
|00Q6000000IZBQZEA5|null                          |
|00Q6000000IZNP4EAP|null                          |
The documentation specifies that fields to be returned from linked objects must be specified in the following manner...
To retrieve a column from a linked module, it is necessary to define the column in a particular manner in the Edit schema view. The correct syntax is:

And you can see from the LogRow output that I have tried that here, however I can not get any results for the Subject field no matter what I try.
My sense is that I am simply not correctly specifying the field(s) that I want in the schema (but I could be wrong about that), but I am at a loss as to what to try.  I am not sure if this is relevant but the Subject field that I am after will return what looks like a JSON object.
Anyone have any insight as to how to specify the Subject field here (or what else might be the problem)?  
Thanks in advance.  Any insight is greatly appreciated.
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Re: Retrieving values form Salesforce Activity History

Try to call the column as "Activity_records_Subject" as you are in a master-detail relationship.
Have a look to this link
Hope this helps,