Revert "Return empty DataTable from GetSchemaTable. (#419)" (#696)

Author: cheenamalhotra

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlDataReader.cs

@@ -1454,7 +1454,7 @@ public override DataTable GetSchemaTable()
                         Debug.Assert(null != _metaData.schemaTable, "No schema information yet!");
                     }
                 }
-                return _metaData?.schemaTable ?? new DataTable();
+                return _metaData?.schemaTable;
             }
             finally
             {

src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/SqlDataReader.cs

@@ -1681,10 +1681,9 @@ override public DataTable GetSchemaTable()
                     {
                         _metaData.schemaTable = BuildSchemaTable();
                         Debug.Assert(null != _metaData.schemaTable, "No schema information yet!");
-                        // filter table?
                     }
                 }
-                return _metaData?.schemaTable ?? new DataTable();
+                return _metaData?.schemaTable;
             }
             finally
             {

src/Microsoft.Data.SqlClient/tests/ManualTests/SQL/DataReaderTest/DataReaderTest.cs

@@ -38,6 +38,7 @@ public static void LoadReaderIntoDataTableToTestGetSchemaTable()
         [ConditionalFact(typeof(DataTestUtility), nameof(DataTestUtility.AreConnStringsSetup))]
         public static void MultiQuerySchema()
         {
+            SqlConnectionStringBuilder builder = new SqlConnectionStringBuilder(DataTestUtility.TCPConnectionString);
             using (SqlConnection connection = new SqlConnection(DataTestUtility.TCPConnectionString))
             {
                 connection.Open();
@@ -66,25 +67,7 @@ public static void MultiQuerySchema()
             }
         }
 
-        [ConditionalFact(typeof(DataTestUtility), nameof(DataTestUtility.AreConnStringsSetup))]
-        public static void GetSchemaTable_returns_null_when_no_resultset()
-        {
-            using (SqlConnection connection = new SqlConnection(DataTestUtility.TCPConnectionString))
-            {
-                connection.Open();
 
-                using (SqlCommand command = connection.CreateCommand())
-                {
-                    command.CommandText = "SELECT 1";
-                    using (SqlDataReader reader = command.ExecuteReader())
-                    {
-                        reader.NextResult();
-                        Assert.NotNull(reader.GetSchemaTable());
-                    }
-                }
-            }
-        }
-        
         // Checks for the IsColumnSet bit in the GetSchemaTable for Sparse columns
         [ConditionalFact(typeof(DataTestUtility), nameof(DataTestUtility.AreConnStringsSetup))]
         public static void CheckSparseColumnBit()