Fixed empty subjects and wrong link in readme

README.md

@@ -65,7 +65,7 @@ Some features rely on having an SMTP email service set up, and won't be availabl
 * Send document to email.
 * Recover user password.
 
-You can use any email service that allow sending emails using the SMTP protocol, like [GMX](gmx.com). The following environment variables need to be defined:
+You can use any email service that allow sending emails using the SMTP protocol, like [GMX](https://gmx.com/mail). The following environment variables need to be defined:
 
 * `SMTP_SERVER`: The URL of the SMTP server to be used, for example `mail.gmx.com`.
 * `SMTP_PORT`: The port number used by the email service, defaults to `587`.

internal/metadata/epub.go

@@ -52,6 +52,10 @@ func (e EpubReader) Metadata(file string) (Metadata, error) {
 	var subjects []string
 	if len(opf.Metadata.Subject) > 0 {
 		for _, subject := range opf.Metadata.Subject {
+			subject.Value = strings.TrimSpace(subject.Value)
+			if subject.Value == "" {
+				continue
+			}
 			// Some epub files mistakenly put all subjects in a single field instead of using a field for each one.
 			// We want to identify those cases looking for specific separators and then indexing each subject properly.
 			names := strings.Split(subject.Value, ",")