Fixes slight issue with timestamp validation

src/service/clmcservice/graphapi/utilities.py

@@ -100,7 +100,7 @@ def validate_json_queries_body(body):
         assert GRAPH_BUILD_SF_QUERY_PARAMS == set(query_data.keys()), "Invalid query data for service function {0} in the JSON query document".format(sf)
 
     assert type(body["from"]) == int, "'from' parameter must be a timestamp integer"
-    assert body["from"] > 0, "'from' parameter must be a positive timestamp integer"
+    assert body["from"] >= 0, "'from' parameter must be a positive timestamp integer or 0"
     assert type(body["to"]) == int, "'to' parameter must be a timestamp integer"
     assert body["to"] > body["from"], "'to' parameter timestamp must be greater than 'from' parameter timestamp"