Fix divide_by_ functions

lib/ip/base.rb

@@ -220,6 +220,7 @@ def split
   # stop when subnets reach their smallest possible size (i.e. 31 for IP4)
   def divide_by_subnets(number_subnets)
     nets = []
+    return nets if split.empty?
     nets << self
     loop do
       new_nets = []
@@ -236,6 +237,7 @@ def divide_by_subnets(number_subnets)
   # subdivide a larger subnet into smaller subnets by number of hosts
   def divide_by_hosts(number_hosts)
     nets = []
+    return nets if split.empty?
     nets << self
     while number_hosts <= (nets[0].split[0].size - 2) &&
           nets[0].pfxlen <= (self.class::ADDR_BITS - 1)

test/ip_test.rb

@@ -174,6 +174,14 @@ class IPTest < Minitest::Test
                      IP.new('1.2.3.0/24').split
       end
 
+      it 'has divide_by_subnets returns empty array when single IPv4' do
+        assert_equal [], IP.new('1.2.3.4').divide_by_subnets(1)
+      end
+
+      it 'has divide_by_subnets returns empty array when single IPv6' do
+        assert_equal [], IP.new('1:0:2:0:0:0:0:0').divide_by_subnets(1)
+      end
+
       it 'has divide_by_subnets be exact' do
         assert_equal [IP.new('1.2.3.0/26'), IP.new('1.2.3.64/26'),
                       IP.new('1.2.3.128/26'), IP.new('1.2.3.192/26')],
@@ -198,6 +206,14 @@ class IPTest < Minitest::Test
                      IP.new('1.2.3.0/24').divide_by_hosts(68)
       end
 
+      it 'has divide_by_hosts returns empty array when single IPv4' do
+        assert_equal [], IP.new('1.2.3.4/32').divide_by_hosts(68)
+      end
+
+      it 'has divide_by_hosts returns empty array when single IPv6' do
+        assert_equal [], IP.new('1:0:2:0:0:0:0:0').divide_by_subnets(1)
+      end
+
       it 'has size' do
         assert_equal 256, @addr.size
       end