Use assumer method instead of null-ignoring operator.

Author: sharpjs

PSql/Commands/ConnectedCmdlet.cs

@@ -1,6 +1,8 @@
 // Copyright Subatomix Research Inc.
 // SPDX-License-Identifier: MIT
 
+using System.Diagnostics;
+
 namespace PSql.Commands;
 
 /// <summary>
@@ -71,4 +73,15 @@ public virtual void Dispose()
         Connection      = null;
         _ownsConnection = false;
     }
+
+#if !DEBUG
+    [ExcludeFromCodeCoverage]
+#endif
+    [Conditional("DEBUG")]
+    [MemberNotNull(nameof(Connection))]
+    protected void AssumeBeginProcessingInvoked()
+    {
+        if (Connection is null)
+            throw new InvalidOperationException("BeginProcessing() has not been invoked.");
+    }
 }

PSql/Commands/InvokeSqlCommand.cs

@@ -118,12 +118,13 @@ private IEnumerator<object> ExecuteAndProjectToObjects(string batch)
     {
         const int DefaultTimeoutSeconds = 30;
 
+        AssumeBeginProcessingInvoked();
+
         var timeout = Timeout.HasValue
             ? (int) Timeout.Value.TotalSeconds
             : DefaultTimeoutSeconds;
 
-        // NULLS: _command created in BeginProcessing
-        return Connection!.InnerConnection.ExecuteAndProjectTo(
+        return Connection.InnerConnection.ExecuteAndProjectTo(
             batch, new PSObjectBuilder(), timeout, UseSqlTypes
         );
     }