fix generate name value for MethodInfo without Parameters (#1789)

* fix generate name value for MethodInfo without Parameters

* add test for XmlDocReader, case: method without input params

Author: hessenar

src/System.CommandLine.DragonFruit.Tests/XmlDocReaderTests.cs

@@ -14,6 +14,10 @@ private class Program
             public static void Main(bool verbose = false, string flavor = null, int? count = 0)
             {
             }
+
+            public static void MainWithoutParam()
+            {
+            }
         }
 
         [Fact]
@@ -46,5 +50,30 @@ public void It_finds_member_xml()
             helpMetadata.ParameterDescriptions["flavor"].Should().Be("Which flavor to use");
             helpMetadata.ParameterDescriptions["count"].Should().Be("How many smoothies?");
         }
+
+        [Fact]
+        public void It_finds_member_without_param()
+        {
+            const string xml = @"<?xml version=""1.0""?>
+<doc>
+    <assembly>
+        <name>DragonFruit</name>
+    </assembly>
+    <members>
+        <member name=""M:System.CommandLine.DragonFruit.Tests." + nameof(XmlDocReaderTests) + @".Program.MainWithoutParam"">
+            <summary>
+            Hello
+            </summary>
+        </member>
+    </members>
+</doc>
+";
+            Action action = Program.MainWithoutParam;
+            var reader = new StringReader(xml);
+            XmlDocReader.TryLoad(reader, out var docReader).Should().BeTrue();
+
+            docReader.TryGetMethodDescription(action.Method, out var helpMetadata).Should().BeTrue();
+            helpMetadata.Description.Should().Be("Hello");
+        }
     }
 }

src/System.CommandLine.DragonFruit/XmlDocReader.cs

@@ -55,26 +55,30 @@ public bool TryGetMethodDescription(MethodInfo info, out CommandHelpMetadata com
             sb.Append("M:");
             AppendTypeName(sb, info.DeclaringType);
             sb.Append(".")
-              .Append(info.Name)
-              .Append("(");
+              .Append(info.Name);
 
-            bool first = true;
-            foreach (ParameterInfo param in info.GetParameters())
+            var parameters = info.GetParameters();
+            if (parameters.Length > 0)
             {
-                if (first)
+                sb.Append("(");
+                bool first = true;
+                foreach (ParameterInfo param in info.GetParameters())
                 {
-                    first = false;
-                }
-                else
-                {
-                    sb.Append(",");
+                    if (first)
+                    {
+                        first = false;
+                    }
+                    else
+                    {
+                        sb.Append(",");
+                    }
+
+                    AppendTypeName(sb, param.ParameterType);
                 }
 
-                AppendTypeName(sb, param.ParameterType);
+                sb.Append(")");
             }
 
-            sb.Append(")");
-
             string name = sb.ToString();
 
             XElement member = _members.Elements("member")