Fixe SonarQube Reliability-Issues S2789, S3077 und S2184

S2789 (32 Stellen): null-Checks auf Optional-Feldern entfernt bzw. durch
Objects.requireNonNullElse(field, Optional.empty()) ersetzt. Die zuvor
defensive Behandlung von null-Optionals erfolgt jetzt ueber den
Bibliotheksaufruf, sodass das Verhalten unveraendert bleibt, aber die
direkte Null-Pruefung gegen Optional entfaellt.

S3077 (5 Stellen): volatile-Felder mit Objekt-Referenzen durch
AtomicReference ersetzt (ScheduledExecutorServiceSchedulerAdapter,
BootstrapRunner.guiApplicationRunContext, PdfPreviewPane.currentDocument/
currentRenderer/currentSourceFile, SingleInstanceGuard.socket). Die
PdfPreviewPane-Felder werden auf JavaFX- bzw. Worker-Thread genutzt;
AtomicReference bietet hier konsistente atomare Publikation ohne
Verhaltensaenderung.

S2184 (3 Stellen): Integer-Division SECONDARY_SPACING / 2 durch
SECONDARY_SPACING / 2.0 ersetzt, damit das Insets-Argument als double
ohne implizite Truncierung berechnet wird.

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/in/HistoricalDocumentContext.java

@@ -1,6 +1,7 @@
 package de.gecheckt.pdf.umbenenner.application.port.in;
 
 import java.time.Instant;
+import java.util.Objects;
 import java.util.Optional;
 
 /**
@@ -37,9 +38,9 @@ public record HistoricalDocumentContext(
      *                              {@code lastFailureInstant} {@code null} sind
      */
     public HistoricalDocumentContext {
-        lastTargetFileName = lastTargetFileName == null ? Optional.empty() : lastTargetFileName;
-        lastSuccessInstant = lastSuccessInstant == null ? Optional.empty() : lastSuccessInstant;
-        lastFailureInstant = lastFailureInstant == null ? Optional.empty() : lastFailureInstant;
+        lastTargetFileName = Objects.requireNonNullElse(lastTargetFileName, Optional.empty());
+        lastSuccessInstant = Objects.requireNonNullElse(lastSuccessInstant, Optional.empty());
+        lastFailureInstant = Objects.requireNonNullElse(lastFailureInstant, Optional.empty());
     }
 
     /**

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/in/SchedulerStatus.java

@@ -1,6 +1,7 @@
 package de.gecheckt.pdf.umbenenner.application.port.in;
 
 import java.time.Instant;
+import java.util.Objects;
 import java.util.Optional;
 
 import de.gecheckt.pdf.umbenenner.application.port.out.RunSummary;
@@ -48,18 +49,10 @@ public record SchedulerStatus(
         if (state == null) {
             throw new IllegalArgumentException("state darf nicht null sein");
         }
-        if (lastRunEndedAt == null) {
-            throw new IllegalArgumentException("lastRunEndedAt darf nicht null sein");
-        }
-        if (lastRunSummary == null) {
-            throw new IllegalArgumentException("lastRunSummary darf nicht null sein");
-        }
-        if (nextTickAt == null) {
-            throw new IllegalArgumentException("nextTickAt darf nicht null sein");
-        }
-        if (lastError == null) {
-            throw new IllegalArgumentException("lastError darf nicht null sein");
-        }
+        Objects.requireNonNull(lastRunEndedAt, "lastRunEndedAt darf nicht null sein");
+        Objects.requireNonNull(lastRunSummary, "lastRunSummary darf nicht null sein");
+        Objects.requireNonNull(nextTickAt, "nextTickAt darf nicht null sein");
+        Objects.requireNonNull(lastError, "lastError darf nicht null sein");
     }
 
     /**

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/EffectiveApiKeyDescriptor.java

@@ -32,7 +32,7 @@ public record EffectiveApiKeyDescriptor(
      */
     public EffectiveApiKeyDescriptor {
         Objects.requireNonNull(origin, "origin must not be null");
-        envVarName = envVarName == null ? Optional.empty() : envVarName;
+        envVarName = Objects.requireNonNullElse(envVarName, Optional.empty());
     }
 
     /**

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogRequest.java

@@ -45,7 +45,7 @@ public record ModelCatalogRequest(
         if (timeoutSeconds <= 0) {
             throw new IllegalArgumentException("timeoutSeconds must be positive, was: " + timeoutSeconds);
         }
-        baseUrl = baseUrl == null ? Optional.empty() : baseUrl;
-        apiKey = apiKey == null ? Optional.empty() : apiKey;
+        baseUrl = Objects.requireNonNullElse(baseUrl, Optional.empty());
+        apiKey = Objects.requireNonNullElse(apiKey, Optional.empty());
     }
 }

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationFinding.java

@@ -38,7 +38,7 @@ public record EditorValidationFinding(
     public EditorValidationFinding {
         Objects.requireNonNull(severity, "severity must not be null");
         Objects.requireNonNull(message, "message must not be null");
-        fieldKey = fieldKey == null ? Optional.empty() : fieldKey;
+        fieldKey = Objects.requireNonNullElse(fieldKey, Optional.empty());
     }
 
     /**

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/technicaltest/CheckpointResult.java

@@ -89,9 +89,7 @@ public sealed interface CheckpointResult
             Objects.requireNonNull(checkpointId, "checkpointId must not be null");
             Objects.requireNonNull(severity, "severity must not be null");
             Objects.requireNonNull(message, "message must not be null");
-            correctionSuggestion = correctionSuggestion == null
-                    ? Optional.empty()
-                    : correctionSuggestion;
+            correctionSuggestion = Objects.requireNonNullElse(correctionSuggestion, Optional.empty());
         }
 
         /**