Make aggregate check input columns.

Author: dgeelen-uipath

QueryBuilder.Tests/AggregateTests.cs

@@ -1,11 +1,18 @@
 using SqlKata.Compilers;
 using SqlKata.Tests.Infrastructure;
+using System;
 using Xunit;
 
 namespace SqlKata.Tests
 {
     public class AggregateTests : TestSupport
     {
+        [Fact]
+        public void AsAggregateEmpty()
+        {
+            Assert.Throws<ArgumentException>(() => new Query("A").AsAggregate("aggregate", new string[] { }));
+        }
+
         [Fact]
         public void Count()
         {

QueryBuilder/Query.Aggregate.cs

@@ -7,6 +7,10 @@ public partial class Query
     {
         public Query AsAggregate(string type, string[] columns = null)
         {
+            if (columns.Count() == 0)
+            {
+                throw new System.ArgumentException("Cannot aggregate without columns");
+            }
 
             Method = "aggregate";