Fix NullReferenceException in GetSchemaTable. Fixes #580

Author: bgrainger

src/MySqlConnector/MySql.Data.MySqlClient/MySqlDataReader.cs

@@ -234,10 +234,7 @@ public override long GetChars(int ordinal, long dataOffset, char[] buffer, int b
 		public override DataTable GetSchemaTable()
 		{
 			if (m_schemaTable == null)
-			{
 				m_schemaTable = BuildSchemaTable();
-			}
-
 			return m_schemaTable;
 		}
 
@@ -309,6 +306,8 @@ internal async Task ReadFirstResultSetAsync(IOBehavior ioBehavior)
 		internal DataTable BuildSchemaTable()
 		{
 			var colDefinitions = GetResultSet().ColumnDefinitions;
+			if (colDefinitions == null)
+				return null;
 			DataTable schemaTable = new DataTable("SchemaTable");
 			schemaTable.Locale = CultureInfo.InvariantCulture;
 			schemaTable.MinimumCapacity = colDefinitions.Length;

tests/SideBySide/DataTypes.cs

@@ -1149,6 +1149,28 @@ public void GetSchemaTableTwice()
 				}
 			}
 		}
+
+		[Fact]
+		public void GetSchemaTableAfterNextResult()
+		{
+			using (var command = Connection.CreateCommand())
+			{
+				command.CommandText = "select Int16 from datatypes_integers;";
+				using (var reader = command.ExecuteReader())
+				{
+					var table = reader.GetSchemaTable();
+					Assert.NotNull(table);
+					Assert.Equal("Int16", table.Rows[0]["ColumnName"]);
+
+					while (reader.Read())
+					{
+					}
+
+					Assert.False(reader.NextResult());
+					Assert.Null(reader.GetSchemaTable());
+				}
+			}
+		}
 #endif
 
 #if !BASELINE