fix null error

Author: adelinowona

src/MongoDB.Driver/PipelineStageDefinitionBuilder.cs

@@ -616,10 +616,8 @@ public static PipelineStageDefinition<TInput, TOutput> Facet<TInput, TOutput>(
         /// <returns>The stage.</returns>
         internal static PipelineStageDefinition<TInput, TOutput> GeoNear<TInput, TPoint, TOutput>(
             TPoint near,
-            GeoNearOptions<TInput> options = null) where TPoint : class
+            GeoNearOptions<TInput> options = null)
         {
-            Ensure.IsNotNull(near, nameof(near));
-            
             const string operatorName = "$geoNear";
             var stage = new DelegatedPipelineStageDefinition<TInput, TOutput>(
                 operatorName,
@@ -661,6 +659,7 @@ public static PipelineStageDefinition<TInput, TOutput> GeoNear<TInput, TCoordina
             GeoNearOptions<TInput> options = null) 
             where TCoordinates : GeoJsonCoordinates
         {
+            Ensure.IsNotNull(near, nameof(near));
             return GeoNear<TInput, GeoJsonPoint<TCoordinates>, TOutput>(near, options);
         }
 
@@ -677,6 +676,7 @@ public static PipelineStageDefinition<TInput, TOutput> GeoNear<TInput, TCoordina
             TCoordinates[] near,
             GeoNearOptions<TInput> options = null)
         {
+            Ensure.IsNotNull(near, nameof(near));
             Ensure.That(near.Length, len => len is >= 2 and <= 3, nameof(near), "Legacy coordinates array should have 2 or 3 coordinates.");
             return GeoNear<TInput, TCoordinates[], TOutput>(near, options);
         }
@@ -693,6 +693,7 @@ public static PipelineStageDefinition<TInput, TOutput> GeoNear<TInput, TOutput>(
             BsonDocument near,
             GeoNearOptions<TInput> options = null)
         {
+            Ensure.IsNotNull(near, nameof(near));
             Ensure.That(near.ElementCount, len => len is >= 2 and <= 3, nameof(near), "Legacy coordinates document should have 2 or 3 coordinates.");
             return GeoNear<TInput, BsonDocument, TOutput>(near, options);
         }

tests/MongoDB.Driver.Tests/PipelineStageDefinitionBuilderTests.cs

@@ -205,6 +205,12 @@ public void GeoNear_with_wrong_legacy_coordinates_should_throw_exception()
                     PipelineStageDefinitionBuilder.GeoNear<BsonDocument, double, BsonDocument>([34.0, 67.0, 23.0, 34.5]);
             });
 
+            Assert.Throws<ArgumentException>(() =>
+            {
+                var result = 
+                    PipelineStageDefinitionBuilder.GeoNear<BsonDocument, double, BsonDocument>([34.0]);
+            });
+            
             Assert.Throws<ArgumentException>(() =>
             {
                 var result =