fix #477 do not render query property on function_score queries if the query is conditionless, omission is sufficient to mean match_all

Author: Mpdreamz

Diff for: src/Nest/DSL/Query/FunctionScoreQueryDescriptor.cs

@@ -49,7 +49,7 @@ public FunctionScoreQueryDescriptor<T> Query(Func<QueryDescriptor<T>, BaseQuery>
             var query = new QueryDescriptor<T>();
             var q = querySelector(query);
 
-            this._Query = q;
+            this._Query = q.IsConditionless ? null : q;
             return this;
         }
 

Diff for: src/Tests/Nest.Tests.Unit/Search/Query/Singles/FunctionScoreQueryJson.cs

@@ -45,5 +45,43 @@ public void FunctionScoreQuery()
 			}";
 			Assert.True(json.JsonEquals(expected), json);
 		}
+		
+		[Test]
+		public void FunctionScoreQueryConditionless()
+		{
+			var s = new SearchDescriptor<ElasticsearchProject>().From(0).Size(10)
+				.Query(q => q
+					.FunctionScore(fs => fs
+						.Query(qq => qq.Term("", ""))
+						.Functions(
+							f => f.Gauss(x => x.StartedOn, d => d.Scale("42w")),
+							f => f.Linear(x => x.FloatValue, d => d.Scale("0.3")),
+							f => f.Exp(x => x.DoubleValue, d => d.Scale("0.5")),
+							f => f.BoostFactor(2)
+						)
+						.ScoreMode(FunctionScoreMode.sum)
+                        .BoostMode(FunctionBoostMode.replace)
+					)
+				).Fields(x => x.Content);
+
+			var json = TestElasticClient.Serialize(s);
+			var expected = @"{ 
+                from: 0, size: 10, 
+				query : {
+                    function_score : { 
+                        functions: [
+                            {gauss:  { startedOn  : { scale: '42w'}}},
+                            {linear: { floatValue : { scale: '0.3'}}},
+                            {exp:    { doubleValue: { scale: '0.5'}}}, 
+                            {boost_factor: 2.0 }
+                        ],				
+                        score_mode: 'sum',
+                        boost_mode: 'replace',
+					}
+				},
+                fields: [""content""]
+			}";
+			Assert.True(json.JsonEquals(expected), json);
+		}
 	}
 }