Make the empty RequestBody explicit

Author: gesellix

api-client/src/main/kotlin/de/gesellix/docker/remote/api/client/ContainerApi.kt

@@ -47,6 +47,7 @@ import kotlinx.coroutines.cancel
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.runBlocking
 import kotlinx.coroutines.withTimeout
+import okhttp3.RequestBody
 import okio.Source
 import okio.source
 import java.io.InputStream
@@ -275,7 +276,7 @@ class ContainerApi(dockerClientConfig: DockerClientConfig = defaultClientConfig,
     stdout: Boolean?,
     stderr: Boolean?
   ): RequestConfig {
-    val localVariableBody = null
+    val localVariableBody = RequestBody.EMPTY
     val localVariableQuery: MultiValueMap = mutableMapOf<String, List<String>>()
       .apply {
         if (detachKeys != null) {