Handle null parameter value. Fixes #126

Author: bgrainger

src/MySqlConnector/MySqlClient/MySqlParameter.cs

@@ -59,7 +59,7 @@ public override void ResetDbType()
 
 		internal void AppendSqlString(BinaryWriter writer, StatementPreparerOptions options)
 		{
-			if (Value == DBNull.Value)
+			if (Value == null || Value == DBNull.Value)
 			{
 				writer.WriteUtf8("NULL");
 			}

tests/SideBySide.New/QueryTests.cs

@@ -219,6 +219,48 @@ public async Task GetName()
 			}
 		}
 
+		[Fact]
+		public async Task ParameterIsNull()
+		{
+			using (var cmd = m_database.Connection.CreateCommand())
+			{
+				cmd.CommandText = @"drop table if exists query_null_parameter;
+create table query_null_parameter(id integer not null primary key, value text);
+insert into query_null_parameter (id, value) VALUES (1, 'one'), (2, 'two'), (3, null);
+";
+				cmd.ExecuteNonQuery();
+			}
+
+			using (var cmd = m_database.Connection.CreateCommand())
+			{
+				cmd.CommandText = "select id, value FROM query_null_parameter where @parameter is null or value = @parameter order by id;";
+				cmd.Parameters.Add(new MySqlParameter { ParameterName = "@parameter", Value = "one" });
+				using (var reader = cmd.ExecuteReader())
+				{
+					Assert.True(await reader.ReadAsync());
+					Assert.Equal(1L, reader.GetInt64(0));
+					Assert.False(await reader.ReadAsync());
+					Assert.False(await reader.NextResultAsync());
+				}
+			}
+
+			using (var cmd = m_database.Connection.CreateCommand())
+			{
+				cmd.CommandText = "select id, value FROM query_null_parameter where @parameter is null or value = @parameter order by id;";
+				cmd.Parameters.Add(new MySqlParameter { ParameterName = "@parameter", Value = null });
+				using (var reader = cmd.ExecuteReader())
+				{
+					Assert.True(await reader.ReadAsync());
+					Assert.Equal(1L, reader.GetInt64(0));
+					Assert.True(await reader.ReadAsync());
+					Assert.Equal(2L, reader.GetInt64(0));
+					Assert.True(await reader.ReadAsync());
+					Assert.Equal(3L, reader.GetInt64(0));
+					Assert.False(await reader.ReadAsync());
+					Assert.False(await reader.NextResultAsync());
+				}
+			}
+		}
 
 		[Fact]
 		public async Task DoubleDispose()