diff --git a/https/apiError.go b/https/apiError.go
index 384e50b..fbea3c6 100644
--- a/https/apiError.go
+++ b/https/apiError.go
@@ -18,6 +18,11 @@ type ApiError struct {
 	Message    string
 }
 
+func (a ApiError) String() string {
+	return fmt.Sprintf(
+		"ApiError[StatusCode=%v, Message=%v]", a.StatusCode, a.Message)
+}
+
 func (a ApiError) Error() string {
 	return fmt.Sprintf("ApiError occurred: %v", a.Message)
 }
diff --git a/https/apiError_test.go b/https/apiError_test.go
index a570cfe..cc179c3 100644
--- a/https/apiError_test.go
+++ b/https/apiError_test.go
@@ -43,6 +43,17 @@ func TestErrorMethod(t *testing.T) {
 	}
 }
 
+func TestStringMethod(t *testing.T) {
+	expected := "ApiError[StatusCode=500, Message=Server Error]"
+	result := ApiError{
+		StatusCode: 500,
+		Message:    "Server Error",
+	}
+	if result.String() != expected {
+		t.Errorf("Failed:\nExpected: %v\nGot: %v", expected, result.Error())
+	}
+}
+
 func TestCorrectMessageWhenDynamicErrorMessageWithStatusCode(t *testing.T) {
 	tpl := "Error: Status Code {$statusCode}"
 
diff --git a/https/callBuilder.go b/https/callBuilder.go
index 23e9b9c..f13063e 100644
--- a/https/callBuilder.go
+++ b/https/callBuilder.go
@@ -40,7 +40,7 @@ type baseUrlProvider func(server string) string
 type CallBuilder interface {
 	AppendPath(path string)
 	AppendTemplateParam(param string)
-	AppendTemplateParams(params any)
+	AppendTemplateParams(params ...any)
 	AppendErrors(errors map[string]ErrorBuilder[error])
 	BaseUrl(arg string)
 	Method(httpMethodName string)
@@ -183,8 +183,8 @@ func (cb *defaultCallBuilder) AppendPath(path string) {
 
 // AppendTemplateParam appends the provided parameter to the existing path in the CallBuilder as a URL template parameter.
 func (cb *defaultCallBuilder) AppendTemplateParam(param string) {
-	if strings.Contains(cb.path, "%v") {
-		cb.path = fmt.Sprintf(cb.path, "/"+url.QueryEscape(param))
+	if index := strings.Index(cb.path, "%v"); index != -1 {
+		cb.path = cb.path[:index] + url.QueryEscape(param) + cb.path[index+len("%v"):]
 	} else {
 		cb.AppendPath(url.QueryEscape(param))
 	}
@@ -192,18 +192,30 @@ func (cb *defaultCallBuilder) AppendTemplateParam(param string) {
 
 // AppendTemplateParams appends the provided parameters to the existing path in the CallBuilder as URL template parameters.
 // It accepts a slice of strings or a slice of integers as the params argument.
-func (cb *defaultCallBuilder) AppendTemplateParams(params any) {
-	reflectValue := reflect.ValueOf(params)
-	if reflectValue.Type().Kind() == reflect.Slice {
-		for i := 0; i < reflectValue.Len(); i++ {
-			innerParam := reflectValue.Index(i).Interface()
-			switch x := innerParam.(type) {
+func (cb *defaultCallBuilder) AppendTemplateParams(params ...any) {
+
+	for _, param := range params {
+		paramValue := reflect.ValueOf(param)
+		if paramValue.Type().Kind() == reflect.Slice {
+			for i := 0; i < paramValue.Len(); i++ {
+				innerParam := paramValue.Index(i).Interface()
+				switch x := innerParam.(type) {
+				case string:
+					cb.AppendTemplateParam(x)
+				case int:
+					cb.AppendTemplateParam(strconv.Itoa(x))
+				default:
+					cb.AppendTemplateParam(FormatAny(x))
+				}
+			}
+		} else {
+			switch x := param.(type) {
 			case string:
 				cb.AppendTemplateParam(x)
 			case int:
 				cb.AppendTemplateParam(strconv.Itoa(x))
 			default:
-				cb.AppendTemplateParam(fmt.Sprintf("%v", x))
+				cb.AppendTemplateParam(FormatAny(x))
 			}
 		}
 	}
@@ -273,7 +285,18 @@ func (cb *defaultCallBuilder) Header(
 	if cb.headers == nil {
 		cb.headers = make(map[string]string)
 	}
-	SetHeaders(cb.headers, strings.ToLower(name), fmt.Sprintf("%v", value))
+	SetHeaders(cb.headers, strings.ToLower(name), FormatAny(value))
+}
+
+func FormatAny(value any) string {
+	if valueBytes, err := json.Marshal(value); err == nil {
+		return sanitizeString(valueBytes)
+	}
+	return ""
+}
+
+func sanitizeString(valueBytes []byte) string {
+	return strings.Trim(string(valueBytes), "\"")
 }
 
 // CombineHeaders combines the provided headers with the existing headers in the CallBuilder.
@@ -454,7 +477,7 @@ func (cb *defaultCallBuilder) validateJson() error {
 		cb.setContentTypeIfNotSet(JSON_CONTENT_TYPE)
 		return nil
 	}
-	cb.Text(fmt.Sprint(cb.jsonData))
+	cb.Text(FormatAny(cb.jsonData))
 	return nil
 }
 
diff --git a/https/callBuilder_test.go b/https/callBuilder_test.go
index f3cb8b4..d726858 100644
--- a/https/callBuilder_test.go
+++ b/https/callBuilder_test.go
@@ -11,6 +11,7 @@ import (
 	"reflect"
 	"strings"
 	"testing"
+	"time"
 )
 
 var ctx = context.Background()
@@ -134,6 +135,31 @@ func TestAppendTemplateParamsIntegers(t *testing.T) {
 	}
 }
 
+func TestAppendTemplateParamsAnySlice(t *testing.T) {
+	request := GetCallBuilder(ctx, "GET", "/template/%v", nil)
+	request.AppendTemplateParams([]any{time.Time{}})
+	_, response, _ := request.CallAsJson()
+
+	expected := 200
+
+	if response.StatusCode != expected {
+		t.Errorf("Failed:\nExpected: %v\nGot: %v", expected, response)
+	}
+}
+
+func TestAppendTemplateParamsAny(t *testing.T) {
+	request := GetCallBuilder(ctx, "GET", "/template/%v", nil)
+	request.AppendTemplateParams(time.Now())
+	request.AppendTemplateParams("abc")
+	request.AppendTemplateParams(2)
+	_, response, _ := request.CallAsJson()
+	expected := 200
+
+	if response.StatusCode != expected {
+		t.Errorf("Failed:\nExpected: %v\nGot: %v", expected, response)
+	}
+}
+
 func TestBaseUrlValue(t *testing.T) {
 	request := GetCallBuilder(ctx, "", "/response/integer", nil)
 	request.BaseUrl("https://github.com/apimatic")
diff --git a/https/fileWrapper.go b/https/fileWrapper.go
index 82666f2..1e2cb33 100644
--- a/https/fileWrapper.go
+++ b/https/fileWrapper.go
@@ -18,6 +18,10 @@ type FileWrapper struct {
 	FileHeaders http.Header
 }
 
+func (f FileWrapper) String() string {
+	return fmt.Sprintf("FileWrapper[FileName=%v]", f.FileName)
+}
+
 // isURL checks if the given parsedPath is a URL
 func isURL(parsedPath *url.URL) bool {
 	return parsedPath.Scheme == "http" || parsedPath.Scheme == "https"
diff --git a/https/fileWrapper_test.go b/https/fileWrapper_test.go
index 71582c7..1f183df 100644
--- a/https/fileWrapper_test.go
+++ b/https/fileWrapper_test.go
@@ -55,6 +55,19 @@ func TestGetFileWithContentTypeFromLocalPath(t *testing.T) {
 	}
 }
 
+func TestGetFileStringFromLocalPath(t *testing.T) {
+	file, err := GetFileWithContentType("../internal/binary.png", "image/png")
+	if err != nil {
+		t.Errorf("GetFile failed: %v", err)
+	}
+
+	if file.String() != "FileWrapper[FileName=binary.png]" ||
+		file.FileHeaders.Get(CONTENT_TYPE_HEADER) != "image/png" ||
+		len(file.File) <= 0 {
+		t.Errorf("Expected Image File not recieved ")
+	}
+}
+
 func TestGetFileErrorParsingUrl(t *testing.T) {
 	_, err := GetFile("")
 	if err == nil {
diff --git a/types/optional.go b/types/optional.go
index 661905b..cd10681 100644
--- a/types/optional.go
+++ b/types/optional.go
@@ -61,3 +61,7 @@ func (o *Optional[T]) UnmarshalJSON(input []byte) error {
 
 	return nil
 }
+
+func (o Optional[T]) MarshalJSON() ([]byte, error) {
+	return json.Marshal(o.value)
+}
diff --git a/types/optional_test.go b/types/optional_test.go
index 6c55193..1b057a5 100644
--- a/types/optional_test.go
+++ b/types/optional_test.go
@@ -66,3 +66,17 @@ func TestUnmarshalJSONError(t *testing.T) {
 		t.Errorf("Failed:\nExpected: Unmarshalling Error \nGot: %v", result)
 	}
 }
+
+func TestMarshalJSON(t *testing.T) {
+	value := "Optional Value"
+	expected := types.Optional[string]{}
+	expected.SetValue(&value)
+	expected.ShouldSetValue(true)
+	optionalBytes, _ := json.Marshal(expected)
+
+	var result string
+	_ = json.Unmarshal(optionalBytes, &result)
+	if value != result {
+		t.Errorf("Failed:\nExpected: %v\nGot: %v", value, result)
+	}
+}
diff --git a/utilities/unionTypeHelper_test.go b/utilities/unionTypeHelper_test.go
index 08731a1..6ff8ad7 100644
--- a/utilities/unionTypeHelper_test.go
+++ b/utilities/unionTypeHelper_test.go
@@ -219,7 +219,7 @@ func TestOneOfDiscriminator(t *testing.T) {
 			discriminators:     []string{"4 wheeler", "2 wheeler"},
 			discriminatorField: "type",
 			testValue:          `{"id":2345,"roof":"BIG","type":"2 wheeler"}`,
-			expectedValue:      `{"id":2345,"roof":"BIG","air_level":{},"type":"2 wheeler"}`,
+			expectedValue:      `{"id":2345,"roof":"BIG","air_level":null,"type":"2 wheeler"}`,
 			expectedType:       &internal.Bike{},
 		},
 		{
@@ -326,7 +326,7 @@ func TestAnyOfDiscriminator(t *testing.T) {
 			discriminators:     []string{"", "2 wheeler"},
 			discriminatorField: "type",
 			testValue:          `{"id":2345,"roof":"BIG","type":"2 wheeler"}`,
-			expectedValue:      `{"id":2345,"roof":"BIG","air_level":{},"type":"2 wheeler"}`,
+			expectedValue:      `{"id":2345,"roof":"BIG","air_level":null,"type":"2 wheeler"}`,
 			expectedType:       &internal.Bike{},
 		},
 	}