Fix/commands null (#3310)

* Return exception when a batch has empty commands list.

* Add tests.

* Add error message to Resources.

* Fixing error in Unit Test. Removing the 's'.

Author: deusanyjunior

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlBatch.cs

@@ -4,6 +4,7 @@
 
 #if NET
 
+using System;
 using System.Collections.Generic;
 using System.Data;
 using System.Data.Common;
@@ -223,6 +224,10 @@ private void SetupBatchCommandExecute()
             {
                 throw ADP.ConnectionRequired(nameof(SetupBatchCommandExecute));
             }
+            if (_commands is null) 
+            {
+                throw ADP.InvalidOperation(StringsHelper.GetString(Strings.ADP_NoSqlBatchCommandList));
+            }
             _batchCommand.Connection = Connection;
             _batchCommand.Transaction = Transaction;
             _batchCommand.SetBatchRPCMode(true, _commands.Count);

src/Microsoft.Data.SqlClient/src/Resources/Strings.Designer.cs

@@ -4740,4 +4740,7 @@
   <data name="ADP_ColumnSchemaMissing1" xml:space="preserve">
     <value>Missing the DataColumn '{0}' for the SourceColumn '{2}'.</value>
   </data>
+  <data name="ADP_NoSqlBatchCommandList" xml:space="preserve">
+    <value>SqlBatchCommand list has not been initialized.</value>
+  </data>
 </root>

src/Microsoft.Data.SqlClient/src/Resources/Strings.resx

@@ -25,6 +25,17 @@ public static void MissingCommandTextThrows()
             }
         }
 
+        [ConditionalFact(typeof(DataTestUtility), nameof(DataTestUtility.AreConnStringsSetup))]
+        public static async Task MissingCommandsThrows()
+        {
+            using (var connection = new SqlConnection(DataTestUtility.TCPConnectionString))
+            using (var batch = new SqlBatch { Connection = connection })
+            {
+                connection.Open();
+                await Assert.ThrowsAsync<InvalidOperationException>(() => batch.ExecuteReaderAsync());
+            }
+        }
+
         [ConditionalFact(typeof(DataTestUtility), nameof(DataTestUtility.AreConnStringsSetup))]
         public static void MissingConnectionThrows()
         {