Revert "Return empty DataTable from GetSchemaTable. (#419)" (#697)

Author: cheenamalhotra

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

@@ -1479,7 +1479,7 @@ 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

@@ -1679,12 +1679,17 @@ override public DataTable GetSchemaTable()
                 {
                     if (null != this.MetaData)
                     {
+
                         _metaData.schemaTable = BuildSchemaTable();
                         Debug.Assert(null != _metaData.schemaTable, "No schema information yet!");
                         // filter table?
                     }
                 }
-                return _metaData?.schemaTable ?? new DataTable();
+                if (null != _metaData)
+                {
+                    return _metaData.schemaTable;
+                }
+                return null;
             }
             finally
             {

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

@@ -37,6 +37,7 @@ 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();
@@ -65,25 +66,7 @@ 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()