Fix handling nil values for optional string array parameters, (#194)

* Fix handling nil values for optional string array parameters,

nil values should be equivalent to an empty string, currently we return an error but Claude passes nil for optional values.

* lint fixes

Author: A-Georgiou

pkg/github/issues_test.go

@@ -468,9 +468,10 @@ func Test_CreateIssue(t *testing.T) {
 				),
 			),
 			requestArgs: map[string]interface{}{
-				"owner": "owner",
-				"repo":  "repo",
-				"title": "Minimal Issue",
+				"owner":     "owner",
+				"repo":      "repo",
+				"title":     "Minimal Issue",
+				"assignees": nil, // Expect no failure with nil optional value.
 			},
 			expectError: false,
 			expectedIssue: &github.Issue{

pkg/github/server.go

@@ -238,6 +238,8 @@ func OptionalStringArrayParam(r mcp.CallToolRequest, p string) ([]string, error)
 	}
 
 	switch v := r.Params.Arguments[p].(type) {
+	case nil:
+		return []string{}, nil
 	case []string:
 		return v, nil
 	case []any: