diff --git a/src/main/kotlin/com/vonage/client/kt/Voice.kt b/src/main/kotlin/com/vonage/client/kt/Voice.kt
index 1534b9c..62af4fa 100644
--- a/src/main/kotlin/com/vonage/client/kt/Voice.kt
+++ b/src/main/kotlin/com/vonage/client/kt/Voice.kt
@@ -34,10 +34,8 @@ class Voice(private val voiceClient: VoiceClient) {
 
         fun sendDtmf(digits: String): DtmfResponse = voiceClient.sendDtmf(callId, digits)
 
-        fun streamAudio(streamUrl: String, loop: Int? = null, level: Double? = null): StreamResponse =
-            if (loop != null && level != null) voiceClient.startStream(callId, streamUrl, loop, level)
-            else if (loop != null) voiceClient.startStream(callId, streamUrl, loop)
-            else voiceClient.startStream(callId, streamUrl)
+        fun streamAudio(streamUrl: String, loop: Int = 1, level: Double = 0.0): StreamResponse =
+            voiceClient.startStream(callId, streamUrl, loop, level)
 
         fun stopStream(): StreamResponse = voiceClient.stopStream(callId)
 
diff --git a/src/test/kotlin/com/vonage/client/kt/AbstractTest.kt b/src/test/kotlin/com/vonage/client/kt/AbstractTest.kt
index 14e0233..5199af9 100644
--- a/src/test/kotlin/com/vonage/client/kt/AbstractTest.kt
+++ b/src/test/kotlin/com/vonage/client/kt/AbstractTest.kt
@@ -188,17 +188,20 @@ abstract class AbstractTest {
 
     protected inline fun <reified E: VonageApiResponseException> assertApiResponseException(
             url: String, requestMethod: HttpMethod, actualCall: () -> Any, status: Int,
-            errorType: String, title: String, detail: String, instance: String): E {
+            errorType: String? = null, title: String? = null,
+            detail: String? = null, instance: String? = null): E {
 
-        mockRequest(requestMethod, url).mockReturn(status, mapOf(
-            "type" to errorType, "title" to title,
-            "detail" to detail, "instance" to instance
-        ))
+        val responseParams = mutableMapOf<String, Any>()
+        if (errorType != null) responseParams["type"] = errorType
+        if (title != null) responseParams["title"] = title
+        if (detail != null) responseParams["detail"] = detail
+        if (instance != null) responseParams["instance"] = instance
 
+        mockRequest(requestMethod, url).mockReturn(status, responseParams)
         val exception = assertThrows<E> { actualCall.invoke() }
 
         assertEquals(status, exception.statusCode)
-        assertEquals(URI.create(errorType), exception.type)
+        assertEquals(if (errorType != null) URI.create(errorType) else null, exception.type)
         assertEquals(title, exception.title)
         assertEquals(instance, exception.instance)
         assertEquals(detail, exception.detail)
diff --git a/src/test/kotlin/com/vonage/client/kt/VoiceTest.kt b/src/test/kotlin/com/vonage/client/kt/VoiceTest.kt
index dd74b46..e12aa1b 100644
--- a/src/test/kotlin/com/vonage/client/kt/VoiceTest.kt
+++ b/src/test/kotlin/com/vonage/client/kt/VoiceTest.kt
@@ -99,6 +99,12 @@ class VoiceTest : AbstractTest() {
         assertEqualsSampleCall(infos[1])
     }
 
+    private fun assertExistingCall404(url: String, requestMethod: HttpMethod, invocation: () -> Any) {
+        assertApiResponseException<VoiceResponseException>(url, requestMethod, invocation, 404,
+            title = "Not Found", detail = "Call $callIdStr doesn't exist."
+        )
+    }
+
     private fun testModifyCall(actionName: String = "transfer", invocation: () -> Unit,
                                nccoAction: Map<String, Any>? = null, nccoUrl: String? = null) {
         mockPut(expectedUrl = callUrl,
@@ -112,21 +118,22 @@ class VoiceTest : AbstractTest() {
             status = 204
         )
         invocation.invoke()
+        assertExistingCall404(callUrl, HttpMethod.PUT, invocation)
     }
 
     private fun testStream(loop: Int = 1, level: Double = 0.0, invocation: (() -> StreamResponse)? = null) {
 
         val message = "Stream ${if (invocation == null) "stopped" else "started"}"
         val expectedResponseParams = mapOf("message" to message, "uuid" to callIdStr)
-        val expectedUrl = "$callUrl/stream"
+        val streamUrl = "$callUrl/stream"
         val response = if (invocation == null) {
-            mockDelete(expectedUrl, expectedResponseParams = expectedResponseParams)
+            mockDelete(streamUrl, expectedResponseParams = expectedResponseParams)
             callObj.stopStream()
         }
         else {
-            mockPut(expectedUrl, status = 200,
+            mockPut(streamUrl, status = 200,
                 expectedRequestParams = mapOf(
-                    "stream_url" to listOf(streamUrl),
+                    "stream_url" to listOf(this.streamUrl),
                     "loop" to loop, "level" to level
                 ),
                 expectedResponseParams = expectedResponseParams
@@ -136,6 +143,9 @@ class VoiceTest : AbstractTest() {
         assertNotNull(response)
         assertEquals(message, response.message)
         assertEquals(callIdStr, response.uuid)
+
+        if (invocation != null) assertExistingCall404(streamUrl, HttpMethod.PUT, invocation)
+        else assertExistingCall404(streamUrl, HttpMethod.DELETE, callObj::stopStream)
     }
 
     private fun testTextToSpeech(expectedRequestParams: Map<String, Any>? = null, invocation: () -> TalkResponse) {
@@ -152,6 +162,11 @@ class VoiceTest : AbstractTest() {
         assertNotNull(response)
         assertEquals(message, response.message)
         assertEquals(callIdStr, response.uuid)
+
+        assertExistingCall404(talkUrl,
+            if (expectedRequestParams != null) HttpMethod.PUT else HttpMethod.DELETE,
+            invocation
+        )
     }
 
     @Test