Allow toAlmostEqual with nulls

src/Assert.hack

@@ -82,11 +82,35 @@ abstract class Assert {
   }
 
   public function assertEqualsWithDelta(
-    num $expected,
-    num $actual,
+    ?num $expected,
+    ?num $actual,
     float $delta,
     string $message = '',
   ): void {
+    if (($actual === null) && ($expected === null)) {
+      return;
+    }
+    if ($actual === null) {
+      throw new ExpectationFailedException(
+        Str\format(
+          "%s\nnull is not equal to %f (with delta %f)",
+          $message,
+          (float) $expected,
+          $delta,
+        )
+      );
+    }
+		if ($expected === null) {
+			throw new ExpectationFailedException(
+				Str\format(
+					"%s\n%f is not equal to null (with delta %f)",
+					$message,
+          (float) $actual,
+					$delta,
+				)
+			);
+		}
+
     if ($actual >= $expected - $delta && $actual <= $expected + $delta) {
       return;
     }

src/ExpectObj.hack

@@ -51,20 +51,20 @@ class ExpectObj<T> extends Assert {
    * and $expected are not within $delta of each other.
    */
   public function toEqualWithDelta(
-    num $expected,
+    ?num $expected,
     float $delta,
     string $msg = '',
     mixed ...$args
-  ): void where T as num {
+  ): void where T as ?num {
     $msg = \vsprintf($msg, $args);
     $this->assertEqualsWithDelta($expected, $this->var, $delta, $msg);
   }
 
   public function toAlmostEqual(
-    num $expected,
+    ?num $expected,
     string $msg = '',
     mixed ...$args
-  ): void where T as num {
+  ): void where T as ?num {
     $msg = \vsprintf($msg, $args);
     $this->toEqualWithDelta(
       $expected,

tests/ExpectObjTest.hack

@@ -57,6 +57,8 @@ final class ExpectObjTest extends HackTest {
     expect(dict[])->toBeType('KeyedContainer');
     expect(array(1, 2, 3))->toContain(2);
     expect(array(1, 2, 3))->toNotContain(7);
+    expect(1)->toAlmostEqual(1);
+    expect(null)->toAlmostEqual(null);
 
     // hack arrays
     expect(keyset[1])->toContain(1);
@@ -134,6 +136,7 @@ final class ExpectObjTest extends HackTest {
       array('toNotBeType', 1, 'int'),
       array('toContain', array(1, 2, 3), 7),
       array('toNotContain', array(1, 2, 3), 2),
+      array('toAlmostEqual', null, 0.0),
 
       // hack arrays
       array('toContain', keyset[1, 2, 3], 7),