fix: Properly handle null header values (#91)

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    resend (0.16.0)
+    resend (0.17.1)
       httparty (>= 0.21.0)
 
 GEM

lib/resend/mailer.rb

@@ -113,6 +113,8 @@ def headers_values(mail)
       unignored_headers(mail).each do |h|
         params[h.name.to_s] = h.unparsed_value
       end
+      # remove nil header values
+      params.delete_if { |_k, v| v.nil? }
       params
     end
 

lib/resend/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Resend
-  VERSION = "0.17.0"
+  VERSION = "0.17.1"
 end

spec/railtie/mailer_spec.rb

@@ -52,6 +52,14 @@ def with_overwritten_headers(to, subject)
     end
   end
 
+  def with_nil_header_values(to, subject)
+    headers["X-Entity-Ref-ID"] = nil
+    mail(to: to, subject: subject) do |format|
+      format.text { render plain: "txt" }
+      format.html { render html: "<p>html</p>".html_safe }
+    end
+  end
+
   def with_attachment(to, subject)
     attachments['invoice.pdf'] = {
       :content => File.read('resources/invoice.pdf'),
@@ -135,7 +143,7 @@ class TestMailerWithDisplayName < TestMailer
     expect(body[:headers]["X-Entity-Ref-ID"]).to eql("123")
   end
 
-  it "#mail properly overwrites #headers" do
+  it "#build_resend_params properly overwrites #headers" do
     message = TestMailer.with_overwritten_headers("[email protected]", "Test!")
     body = @mailer.build_resend_params(message)
     expect(body[:from]).to eql("[email protected]")
@@ -145,4 +153,10 @@ class TestMailerWithDisplayName < TestMailer
     expect(body[:text]).to eql("txt")
     expect(body[:headers]["X-Entity-Ref-ID"]).to eql("overwritten")
   end
+
+  it "#build_resend_params handles nil values" do
+    message = TestMailer.with_nil_header_values("[email protected]", "Test!")
+    body = @mailer.build_resend_params(message)
+    expect(body[:headers]).to be nil
+  end
 end