Script error with when input is empty

#!/bin/bash

echo -n "Enter the domain name and press [ENTER]: "
read domain


result1=`dig +short $domain @4.2.2.1`
revresult1=`host $result1 | cut -f5 -d " "`

echo "test1"

result2=`dig +short $domain @dns1.vistapages.com`
revresult2=`host $result2 | cut -f5 -d " "`

echo "test2"

result3=`dig +short $domain @dns2.vistapages.com`
revresult3=`host $result3 | cut -f5 -d " "`



echo "test3"
result4=`dig +short $domain @ns1.hostmds.com`
revresult4=`host $result4 | cut -f5 -d " "`

echo "test4"
result5=`dig +short $domain @ns1.hostmds.com`
revresult5=`host $result5 | cut -f5 -d " "`

echo "test5"
result6=`dig +short $domain @dns1.hostingplex.com`
revresult6=`host $result6`

echo "test6"
result7=`dig +short $domain @dns2.hostingplex.com`
revresult7=`host $result7`

echo "test7"
echo "================================="

echo " Result at Verizon DNS : $result1"
echo " Reverse at Verizon DNS : $revresult1"

echo "================================="
echo " Result at dns1.vistapages.com  : $result2"
echo " Reverse at dns1.vistapages.com : $revresult2"
echo "================================="

echo " Result at dns2.vistapages.com : $result3"
echo " Reverse at dns2.vistapages.com : $revresult3"

echo "================================="

echo " Result at ns1.hostmds.com : $result4"
echo " Reverse at ns1.hostmds.com : $revresult4"

echo "================================="
echo " Result at ns2.hostmds.com : $result5"
echo " Reverse at ns2.hostmds.com : $revresult5"

echo "================================="

echo " Result at dns1.hostingplex.com : $result6"
echo " Reverse at dns1.hostingplex.com  : $revresult6"
echo "================================="


echo " Result at dns2.hostingplex.com : $result7"
echo " Reverse at dns2.hostingplex.com : $revresult1"

Enter the domain name and press [ENTER]: test.com
test1
Usage: host [-aCdlriTwv] [-c class] [-N ndots] [-t type] [-W time]
            [-R number] hostname [server]
       -a is equivalent to -v -t *
       -c specifies query class for non-IN data
       -C compares SOA records on authoritative nameservers
       -d is equivalent to -v
       -l lists all hosts in a domain, using AXFR
       -i IP6.INT reverse lookups
       -N changes the number of dots allowed before root lookup is done
       -r disables recursive processing
       -R specifies number of retries for UDP packets
       -t specifies the query type
       -T enables TCP/IP mode
       -v enables verbose output
       -w specifies to wait forever for a reply
       -W specifies how long to wait for a reply
       -4 use IPv4 query transport only
       -6 use IPv6 query transport only
       -s a SERVFAIL response should stop query
test2
Usage: host [-aCdlriTwv] [-c class] [-N ndots] [-t type] [-W time]
            [-R number] hostname [server]
       -a is equivalent to -v -t *
       -c specifies query class for non-IN data
       -C compares SOA records on authoritative nameservers
       -d is equivalent to -v
       -l lists all hosts in a domain, using AXFR
       -i IP6.INT reverse lookups
       -N changes the number of dots allowed before root lookup is done
       -r disables recursive processing
       -R specifies number of retries for UDP packets
       -t specifies the query type
       -T enables TCP/IP mode
       -v enables verbose output
       -w specifies to wait forever for a reply
       -W specifies how long to wait for a reply
       -4 use IPv4 query transport only
       -6 use IPv6 query transport only
       -s a SERVFAIL response should stop query
test3
Usage: host [-aCdlriTwv] [-c class] [-N ndots] [-t type] [-W time]
            [-R number] hostname [server]
       -a is equivalent to -v -t *
       -c specifies query class for non-IN data
       -C compares SOA records on authoritative nameservers
       -d is equivalent to -v
       -l lists all hosts in a domain, using AXFR
       -i IP6.INT reverse lookups
       -N changes the number of dots allowed before root lookup is done
       -r disables recursive processing
       -R specifies number of retries for UDP packets
       -t specifies the query type
       -T enables TCP/IP mode
       -v enables verbose output
       -w specifies to wait forever for a reply
       -W specifies how long to wait for a reply
       -4 use IPv4 query transport only
       -6 use IPv6 query transport only
       -s a SERVFAIL response should stop query
test4
Usage: host [-aCdlriTwv] [-c class] [-N ndots] [-t type] [-W time]
            [-R number] hostname [server]
       -a is equivalent to -v -t *
       -c specifies query class for non-IN data
       -C compares SOA records on authoritative nameservers
       -d is equivalent to -v
       -l lists all hosts in a domain, using AXFR
       -i IP6.INT reverse lookups
       -N changes the number of dots allowed before root lookup is done
       -r disables recursive processing
       -R specifies number of retries for UDP packets
       -t specifies the query type
       -T enables TCP/IP mode
       -v enables verbose output
       -w specifies to wait forever for a reply
       -W specifies how long to wait for a reply
       -4 use IPv4 query transport only
       -6 use IPv6 query transport only
       -s a SERVFAIL response should stop query
test5
test6
test7
=================================
 Result at Verizon DNS : 205.178.152.103
 Reverse at Verizon DNS : w2k3-cfm3.prod.netsolhost.com.
=================================
 Result at dns1.vistapages.com  : 
 Reverse at dns1.vistapages.com : 
=================================
 Result at dns2.vistapages.com : 
 Reverse at dns2.vistapages.com : 
=================================
 Result at ns1.hostmds.com : 
 Reverse at ns1.hostmds.com : 
=================================
 Result at ns2.hostmds.com : 
 Reverse at ns2.hostmds.com : 
=================================
 Result at dns1.hostingplex.com : 208.83.209.12
 Reverse at dns1.hostingplex.com  : 12.209.83.208.in-addr.arpa domain name pointer 208-83-209-12.mdswireless.com.
=================================
 Result at dns2.hostingplex.com : 208.83.209.12
 Reverse at dns2.hostingplex.com : w2k3-cfm3.prod.netsolhost.com.