[cmdpal] Fix calculator error when pressing Space (#39679)

Co-authored-by: Yu Leng (from Dev Box) <yuleng@microsoft.com>

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Calc/Helper/CalculateHelper.cs

@@ -35,7 +35,7 @@ public static class CalculateHelper
     {
         if (string.IsNullOrWhiteSpace(input))
         {
-            throw new ArgumentNullException(paramName: nameof(input));
+            return false;
         }
 
         if (!RegValidExpressChar.IsMatch(input))

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Calc/Helper/QueryHelper.cs

@@ -32,6 +32,11 @@ public static partial class QueryHelper
         NumberTranslator translator = NumberTranslator.Create(inputCulture, new CultureInfo("en-US"));
         var input = translator.Translate(query.Normalize(NormalizationForm.FormKC));
 
+        if (string.IsNullOrWhiteSpace(input))
+        {
+            return ErrorHandler.OnError(isFallbackSearch, query, Properties.Resources.calculator_expression_empty);
+        }
+
         if (!CalculateHelper.InputValid(input))
         {
             return null;

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Calc/Properties/Resources.Designer.cs

@@ -132,6 +132,15 @@ namespace Microsoft.CmdPal.Ext.Calc.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Please enter an expression.
+        /// </summary>
+        public static string calculator_expression_empty {
+            get {
+                return ResourceManager.GetString("calculator_expression_empty", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Expression wrong or incomplete.
         /// </summary>

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Calc/Properties/Resources.resx

@@ -199,4 +199,7 @@
   <data name="calculator_copy_binary" xml:space="preserve">
     <value>Copy binary</value>
   </data>
+  <data name="calculator_expression_empty" xml:space="preserve">
+    <value>Please enter an expression</value>
+  </data>
 </root>