Fix exception when OUT parameter is NULL. Fixes #425

Author: bgrainger

src/MySqlConnector/Core/StoredProcedureCommandExecutor.cs

@@ -102,7 +102,7 @@ internal void SetParams()
 				for (var i = 0; i < m_outParams.Count; i++)
 				{
 					var param = m_outParams[i];
-					if (param.HasSetDbType)
+					if (param.HasSetDbType && !reader.IsDBNull(i))
 					{
 						var dbTypeMapping = TypeMapper.Instance.GetDbTypeMapping(param.DbType);
 						if (dbTypeMapping != null)

tests/SideBySide/StoredProcedureFixture.cs

@@ -55,6 +55,15 @@ OUT value VARCHAR(100)
 				BEGIN
 					SELECT 'test value' INTO value;
 				END");
+			Connection.Execute(@"DROP PROCEDURE IF EXISTS out_null;
+				CREATE PROCEDURE out_null(
+					OUT string_value VARCHAR(100),
+					OUT int_value INT
+				)
+				BEGIN
+					SELECT NULL INTO string_value;
+					SELECT NULL INTO int_value;
+				END");
 			Connection.Execute(@"drop table if exists sproc_multiple_rows;
 				create table sproc_multiple_rows (
 					value integer not null primary key auto_increment,

tests/SideBySide/StoredProcedureTests.cs

@@ -135,6 +135,36 @@ public async Task StoredProcedureOutIncorrectType()
 			}
 		}
 
+		[Fact]
+		public async Task StoredProcedureReturnsNull()
+		{
+			using (var cmd = m_database.Connection.CreateCommand())
+			{
+				cmd.CommandText = "out_null";
+				cmd.CommandType = CommandType.StoredProcedure;
+				cmd.Parameters.Add(new MySqlParameter
+				{
+					ParameterName = "@string_value",
+					DbType = DbType.String,
+					Direction = ParameterDirection.Output,
+					IsNullable = true,
+					Value = "non null",
+				});
+				cmd.Parameters.Add(new MySqlParameter
+				{
+					ParameterName = "@int_value",
+					DbType = DbType.Int32,
+					Direction = ParameterDirection.Output,
+					IsNullable = true,
+					Value = "123",
+				});
+				await cmd.ExecuteNonQueryAsync();
+
+				Assert.Equal(DBNull.Value, cmd.Parameters["@string_value"].Value);
+				Assert.Equal(DBNull.Value, cmd.Parameters["@int_value"].Value);
+			}
+		}
+
 		[Theory]
 		[InlineData("NonQuery")]
 		[InlineData("Scalar")]