improve crud error messages (#425)

Co-authored-by: Clemens Portele <[email protected]>

Author: azahnen

xtraplatform-features-sql/src/main/java/de/ii/xtraplatform/features/sql/domain/FeatureProviderSql.java

@@ -931,9 +931,6 @@ public boolean supportsMutationsInternal() {
       return false;
     }
     if (!getData().getDatasetChanges().isModeCrud()) {
-      LOGGER.warn(
-          "Feature provider with id '{}' does not support mutations: datasetChanges.mode is not 'CRUD'",
-          getId());
       return false;
     }
 
@@ -1340,10 +1337,17 @@ private MutationResult writeFeatures(
             .withResult((Builder) builder)
             .handleError(
                 (result, throwable) -> {
-                  Throwable error =
-                      throwable instanceof PSQLException || throwable instanceof JsonParseException
-                          ? new IllegalArgumentException(throwable.getMessage())
-                          : throwable;
+                  Throwable error = throwable;
+
+                  if (throwable instanceof PSQLException
+                      || throwable instanceof JsonParseException) {
+                    error =
+                        new IllegalArgumentException(
+                            "Invalid feature data. You may be able to obtain more information about the problem by adding the header ‘Prefer: handling=strict’ to the request.",
+                            throwable);
+                    LogContext.errorAsDebug(LOGGER, throwable, "Error during feature mutation");
+                  }
+
                   return result.error(error);
                 })
             .handleItem((Builder::addIds))