Refactor ReadReceiverNameQuery and improve validation

- Removed parameters from ReadReceiverNameQuery, simplifying its structure.
- Added null check for EmailAddress in GetReceiverName method to enhance input validation.

EnvelopeGenerator.Application/Envelopes/Queries/ReceiverName/ReadReceiverNameQuery.cs

@@ -6,8 +6,6 @@ namespace EnvelopeGenerator.Application.Envelopes.Queries.ReceiverName;
 /// Eine Abfrage, um die zuletzt verwendete Anrede eines Empfängers zu ermitteln, 
 /// damit diese für zukünftige Umschläge wiederverwendet werden kann.
 /// </summary>
-/// <param name="Envelope">Der Umschlag, für den die Anrede des Empfängers ermittelt werden soll.</param>
-/// <param name="OnlyLast">Gibt an, ob nur die zuletzt verwendete Anrede zurückgegeben werden soll.</param>
-public record ReadReceiverNameQuery(EnvelopeQuery? Envelope = null, bool OnlyLast = true) : ReadReceiverQuery
+public record ReadReceiverNameQuery() : ReadReceiverQuery
 {
 }

EnvelopeGenerator.GeneratorAPI/Controllers/EnvelopeReceiverController.cs

@@ -125,6 +125,9 @@ public class EnvelopeReceiverController : ControllerBase
     [HttpGet("salute")]
     public async Task<IActionResult> GetReceiverName([FromQuery] ReadReceiverNameQuery receiverName)
     {
+        if (receiverName.EmailAddress is null)
+            return BadRequest();
+
         return await _erService.ReadLastUsedReceiverNameByMail(receiverName.EmailAddress).ThenAsync(
                         Success: res => res is null ? Ok(string.Empty) : Ok(res),
                         Fail: IActionResult (msg, ntc) =>