The alias value is not properly set when migrating content from D7

Migrating forward statistics gives you:

[error]  Migration failed with source plugin exception: SQLSTATE[23000]: Integrity constraint violation: 1052 Column 'nid' in on clause is ambiguous:
SELECT f.nid AS nid, f.last_forward_timestamp AS last_forward_timestamp, f.forward_count AS forward_count, f.clickthrough_count AS clickthrough_count, n.type AS type, map.sourceid1 AS migrate_map_sourceid1, map.source_row_status AS migrate_map_source_row_status
FROM
{forward_statistics} f
INNER JOIN {node} n ON f.nid = n.nid
LEFT OUTER JOIN www_example_com.migrate_map_forward_statistics map ON
  nid = map.sourceid1
WHERE (map.sourceid1 IS NULL) OR (map.source_row_status = :db_condition_placeholder_0)
ORDER BY nid ASC;