Fix bug wit null element in diff

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 All notable changes to `period` will be documented in this file
 
+## 1.1.1 - 2019-02-01
+
+- Fix bug with null element in diff
+
 ## 1.1.0 - 2019-01-26
 
 - Make Period iterable

src/Period.php

@@ -417,7 +417,11 @@ public function diff(Period ...$periods): PeriodCollection
         if (count($periods) === 1 && ! $this->overlapsWith($periods[0])) {
             $collection = new PeriodCollection();
 
-            $collection[] = $this->gap($periods[0]);
+            $gap = $this->gap($periods[0]);
+
+            if ($gap !== null) {
+                $collection[] = $gap;
+            }
 
             return $collection;
         }

tests/PeriodTest.php

@@ -33,12 +33,12 @@ public function it_can_determine_if_two_periods_touch_each_other()
     {
         $this->assertTrue(
             Period::make('2018-01-01', '2018-01-01')
-              ->touchesWith(Period::make('2018-01-02', '2018-01-02'))
+                ->touchesWith(Period::make('2018-01-02', '2018-01-02'))
         );
 
         $this->assertTrue(
             Period::make('2018-01-02', '2018-01-02')
-              ->touchesWith(Period::make('2018-01-01', '2018-01-01'))
+                ->touchesWith(Period::make('2018-01-01', '2018-01-01'))
         );
 
         $this->assertFalse(
@@ -48,7 +48,7 @@ public function it_can_determine_if_two_periods_touch_each_other()
 
         $this->assertFalse(
             Period::make('2018-01-03', '2018-01-03')
-              ->touchesWith(Period::make('2018-01-01', '2018-01-01'))
+                ->touchesWith(Period::make('2018-01-01', '2018-01-01'))
         );
     }
 
@@ -523,6 +523,18 @@ public function its_iterator_returns_immutable_dates()
         $this->assertInstanceOf(DateTimeImmutable::class, current($period));
     }
 
+    /** @test */
+    public function diff_filters_out_null_object_if_no_gap()
+    {
+        $a = Period::make('2019-02-01', '2019-02-01');
+
+        $b = Period::make('2019-02-02', '2019-02-02');
+
+        $diff = $a->diff($b);
+
+        $this->assertEmpty($diff);
+    }
+
     public function expectedPeriodLengths()
     {
         return [