code: public VirtualMachineScaleSetExtensionInner createOrUpdate(String resourceGroupName, String vmScaleSetName, String vmssExtensionName, VirtualMachineScaleSetExtensionInner extensionParameters) {
          return createOrUpdateWithServiceResponseAsync(resourceGroupName, vmScaleSetName, vmssExtensionName, extensionParameters).toBlocking().last().body();
      }
docs: The operation to create or update an extension.
  
  @param resourceGroupName The name of the resource group.
  @param vmScaleSetName The name of the VM scale set where the extension should be create or updated.
  @param vmssExtensionName The name of the VM scale set extension.
  @param extensionParameters Parameters supplied to the Create VM scale set Extension operation.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @throws CloudException thrown if the request is rejected by server
  @throws RuntimeException all other wrapped checked exceptions if the request fails to be sent
  @return the VirtualMachineScaleSetExtensionInner object if successful.