Annotate nullable WQL helper returns

Agent-Logs-Url: https://github.com/webexpress-framework/WebExpress.WebIndex/sessions/ee1582bc-9681-41fd-b0d1-7d94f2132de5

Co-authored-by: ReneSchwarzer <31061438+ReneSchwarzer@users.noreply.github.com>

Author: Copilot

src/WebExpress.WebIndex/Wql/Function/WqlExpressionNodeFilterFunctionLower.cs

@@ -47,10 +47,11 @@ public override Expression ToExpression(ParameterExpression param)
             return Expression.Call(EvaluateMethod, Expression.Convert(valueExpression, typeof(object)));
         }
 
-        [return: System.Diagnostics.CodeAnalysis.MaybeNull]
-        private static string Evaluate(object value)
+#nullable enable
+        private static string? Evaluate(object value)
         {
             return value?.ToString()?.ToLowerInvariant();
         }
+#nullable restore
     }
 }

src/WebExpress.WebIndex/Wql/Function/WqlExpressionNodeFilterFunctionTrim.cs

@@ -47,10 +47,11 @@ public override Expression ToExpression(ParameterExpression param)
             return Expression.Call(EvaluateMethod, Expression.Convert(valueExpression, typeof(object)));
         }
 
-        [return: System.Diagnostics.CodeAnalysis.MaybeNull]
-        private static string Evaluate(object value)
+#nullable enable
+        private static string? Evaluate(object value)
         {
             return value?.ToString()?.Trim();
         }
+#nullable restore
     }
 }

src/WebExpress.WebIndex/Wql/Function/WqlExpressionNodeFilterFunctionUpper.cs

@@ -48,10 +48,11 @@ public override Expression ToExpression(ParameterExpression param)
             return Expression.Call(EvaluateMethod, Expression.Convert(valueExpression, typeof(object)));
         }
 
-        [return: System.Diagnostics.CodeAnalysis.MaybeNull]
-        private static string Evaluate(object value)
+#nullable enable
+        private static string? Evaluate(object value)
         {
             return value?.ToString()?.ToUpperInvariant();
         }
+#nullable restore
     }
 }