Incorrect MIME boundary generation for Mailable with empty html body

[AntonioDiPassio-AppSys]

• Laravel Version: 8.22.1
• PHP Version: 7.4.11
• Database Driver & Version:

Description:

When sending a Mailable with an empty string as html body, the MIME boundary for the attachment is incorrectly generated.

Steps To Reproduce:

• Create a test.txt file in storage, with some data
• Create a mailable with the following code as build():

        return $this->html('')
            ->subject('test')
            ->attachFromStorage('test.txt');

[driesvints]

@AntonioDiPassio-AppSys can you try to apply the same fix from 0557622 but then for the HTML part a bit above it? Does that fixes your issue?

[AntonioDiPassio-AppSys]

@driesvints Yes, this fixes the issue.