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java.lang.IllegalArgumentException: Illegal group reference	at java.util.regex.Matcher.appendReplacement(Matcher.java:808)	at org.apache.commons.mail.ImageHtmlEmail.replacePattern(ImageHtmlEmail.java:180)	at org.apache.commons.mail.ImageHtmlEmail.buildMimeMessage(ImageHtmlEmail.java:103)	at org.apache.commons.mail.Email.send(Email.java:1427)	at EmailSender.sendHTMLEmail(EmailSender.java:93)	at EmailSenderTest.testImageHtmlEmailDollarBackslash(EmailSenderTest.java:801)