send-email tests: test for boolean variables without a value

The Git.pm code does its own Perl-ifying of boolean variables, let's
ensure that empty values = true for boolean variables, as in the C
code.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9001-send-email.sh

@@ -1368,6 +1368,16 @@ test_expect_success $PREREQ 'sendemail.identity: bool variable fallback' '
 	! grep "X-Mailer" stdout
 '
 
+test_expect_success $PREREQ 'sendemail.identity: bool variable without a value' '
+	git -c sendemail.xmailer \
+		send-email \
+		--dry-run \
+		--from="nobody@example.com" \
+		$patches >stdout &&
+	grep "To: default@example.com" stdout &&
+	grep "X-Mailer" stdout
+'
+
 test_expect_success $PREREQ '--no-to overrides sendemail.to' '
 	git send-email \
 		--dry-run \
@@ -2092,6 +2102,18 @@ test_expect_success $PREREQ '--[no-]xmailer with sendemail.xmailer=true' '
 	do_xmailer_test 1 "--xmailer"
 '
 
+test_expect_success $PREREQ '--[no-]xmailer with sendemail.xmailer' '
+	test_when_finished "test_unconfig sendemail.xmailer" &&
+	cat >>.git/config <<-\EOF &&
+	[sendemail]
+		xmailer
+	EOF
+	test_config sendemail.xmailer true &&
+	do_xmailer_test 1 "" &&
+	do_xmailer_test 0 "--no-xmailer" &&
+	do_xmailer_test 1 "--xmailer"
+'
+
 test_expect_success $PREREQ '--[no-]xmailer with sendemail.xmailer=false' '
 	test_config sendemail.xmailer false &&
 	do_xmailer_test 0 "" &&
@@ -2099,6 +2121,13 @@ test_expect_success $PREREQ '--[no-]xmailer with sendemail.xmailer=false' '
 	do_xmailer_test 1 "--xmailer"
 '
 
+test_expect_success $PREREQ '--[no-]xmailer with sendemail.xmailer=' '
+	test_config sendemail.xmailer "" &&
+	do_xmailer_test 0 "" &&
+	do_xmailer_test 0 "--no-xmailer" &&
+	do_xmailer_test 1 "--xmailer"
+'
+
 test_expect_success $PREREQ 'setup expected-list' '
 	git send-email \
 	--dry-run \