Return empty DataTable from GetSchemaTable. (#419)

Author: ErikEJ

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

@@ -1476,7 +1476,7 @@ public override DataTable GetSchemaTable()
                         Debug.Assert(null != _metaData.schemaTable, "No schema information yet!");
                     }
                 }
-                return _metaData?.schemaTable;
+                return _metaData?.schemaTable ?? new DataTable();
             }
             finally
             {

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

@@ -1667,17 +1667,12 @@ override public DataTable GetSchemaTable()
                 {
                     if (null != this.MetaData)
                     {
-
                         _metaData.schemaTable = BuildSchemaTable();
                         Debug.Assert(null != _metaData.schemaTable, "No schema information yet!");
                         // filter table?
                     }
                 }
-                if (null != _metaData)
-                {
-                    return _metaData.schemaTable;
-                }
-                return null;
+                return _metaData?.schemaTable ?? new DataTable();
             }
             finally
             {

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

@@ -36,7 +36,6 @@ public static void LoadReaderIntoDataTableToTestGetSchemaTable()
         [CheckConnStrSetupFact]
         public static void MultiQuerySchema()
         {
-            SqlConnectionStringBuilder builder = new SqlConnectionStringBuilder(DataTestUtility.TCPConnectionString);
             using (SqlConnection connection = new SqlConnection(DataTestUtility.TCPConnectionString))
             {
                 connection.Open();
@@ -65,7 +64,25 @@ public static void MultiQuerySchema()
             }
         }
 
+        [CheckConnStrSetupFact]
+        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
         [CheckConnStrSetupFact]
         public static void CheckSparseColumnBit()