Usage Example
    This processor pulls data from Solr collections. For its usage, Solr collections
    have to fulfil two requirements:
    - The documents must include a date field containing the time when they were
        indexed. Such kind of field can be easily added to documents at indexing time
        e. g. using Solrs' UpdateRequestProcessor created by
        'TimestampUpdateProcessorFactory'.
- The configuration of the Solr index (e. g. schema.xml or managed-schema) must
        define a uniqueKey field.
    Backwards compatibility to configurations of the GetSolr processor used within releases
    of NiFi prior to 1.5 can be realized as follows:
    - Find the file conf/.getSolr* within the prior NiFi installation.
- Open the file and copy the timestamp defined for 'LastEndDate'.
- Insert the timestamp into the field 'Initial Date Filter'.
    Annotation: The value of property 'Solr Query' actually is not added to parameter 'q'
    but to parameter 'fq' for two reasons:
    - Improving performance by leveraging Solrs' filter cache.
- Scoring is not required for the purpose of this processor as the sorting
        is fixed to 'DateField asc, IdField asc'