Alert-Info Header in none is sending Alert-Info: instead of nothing

Hello,

The default Alert-Info header is 'none' and never the less it is being added to the SIP headers. Even when I am setting the field to custom with an empty string it is added like this in a call forward scenario to another trunk:
{{}}

{{}}

Alert-Info: 
Alert-Info: 
Alert-Info: 
Alert-Info: 

or

Alert-Info: custom
Alert-Info: custom
Alert-Info: custom
Alert-Info: custom

{{}}

{{}}Here is the full header:

Audio is at 10608
Adding codec alaw to SDP
Adding codec ulaw to SDP
Adding non-codec 0x1 (telephone-event) to SDP
Reliably Transmitting (no NAT) to 82.166.66.147:5060:
INVITE sip:0747604197@82.166.66.147 SIP/2.0
Via: SIP/2.0/UDP 192.116.49.67:5060;branch=z9hG4bK5f10e292
Max-Forwards: 70
From: <sip:0737801905@192.116.49.67>;tag=as515270dc
To: <sip:0747604197@82.166.66.147>
Contact: <sip:0737801905@192.116.49.67:5060>
Call-ID: 77c3a8091f227dc9452201a500bbffb3@192.116.49.67:5060
CSeq: 102 INVITE
User-Agent: FPBX-13.0.195.4(13.19.1)
Date: Wed, 25 Jul 2018 16:37:26 GMT
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH, MESSAGE
Supported: replaces, timer
Alert-Info: custom
Alert-Info: custom
Alert-Info: custom
Alert-Info: custom
Content-Type: application/sdp
Content-Length: 276v=0
o=root 234168054 234168054 IN IP4 192.116.49.67
s=Asterisk PBX 13.19.1
c=IN IP4 192.116.49.67
t=0 0
m=audio 10608 RTP/AVP 8 0 101
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ptime:20
a=maxptime:150
a=sendrecv---

<--- SIP read from UDP:82.166.66.147:5060 --->
SIP/2.0 400 Bad Request
Via: SIP/2.0/UDP 192.116.49.67:5060;branch=z9hG4bK5f10e292
From: <sip:0737801905@192.116.49.67>;tag=as515270dc
To: <sip:0747604197@82.166.66.147>
Call-ID: 77c3a8091f227dc9452201a500bbffb3@192.116.49.67:5060
CSeq: 102 INVITE
Error-Info: <sip:0747604197@82.166.66.147>;cause="[line 013] SIP syntax error"
Content-Length: 0 

I am bypassing this problem by removing the Alert-Info headers like this:

[macro-dialout-trunk-predial-hook]
exten => s,1,SIPRemoveHeader(Alert-Info:)
exten => s,n,MacroExit()

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Thank you,