CSHARP-4521: Handle parameterName empty string the same as null.

Author: rstam

src/MongoDB.Driver/Linq/Linq3Implementation/Misc/NameGenerator.cs

@@ -25,7 +25,7 @@ internal class NameGenerator
 
         public string GetParameterName(ParameterExpression parameter)
         {
-            if (parameter.Name != null)
+            if (!string.IsNullOrEmpty(parameter.Name))
             {
                 return parameter.Name;
             }

tests/MongoDB.Driver.Tests/Linq/Linq3ImplementationTests/Jira/CSharp4521Tests.cs

@@ -0,0 +1,67 @@
+/* Copyright 2010-present MongoDB Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System;
+using System.Linq;
+using System.Linq.Expressions;
+using FluentAssertions;
+using MongoDB.Driver.Linq;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Linq.Linq3ImplementationTests.Jira
+{
+    public class CSharp4512Tests : Linq3IntegrationTest
+    {
+        [Theory]
+        [InlineData("x")]
+        [InlineData("")]
+        [InlineData(null)]
+        public void Where_should_work(string paramName)
+        { 
+            var collection = CreateCollection();
+            var param = Expression.Parameter(typeof(C), paramName);
+            var body = Expression.MakeBinary(
+                ExpressionType.Equal,
+                Expression.Property(param, "Id"),
+                Expression.Constant(1));
+            var predicate = Expression.Lambda<Func<C, bool>>(body, param);
+
+            var queryable = collection.AsQueryable().Where(predicate);
+
+            var stages = Translate(collection, queryable);
+            AssertStages(stages, "{ $match : { _id : 1 } }");
+
+            var results = queryable.ToList();
+            results.Select(x => x.Id).Should().Equal(1);
+        }
+
+        private IMongoCollection<C> CreateCollection()
+        {
+            var collection = GetCollection<C>("C");
+
+            CreateCollection(
+                collection,
+                new C { Id = 1 },
+                new C { Id = 2 });
+
+            return collection;
+        }
+
+        private class C
+        {
+            public int Id { get; set; }
+        }
+    }
+}