Fix IF implementation to comply with Excel behavior

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 ### Fixed
 
+- IF implementation properly handles the value `#N/A` 
 - ...
 
 ## [1.9.0] - 2019-08-17

src/PhpSpreadsheet/Calculation/Logical.php

@@ -266,6 +266,10 @@ public static function NOT($logical = false)
      */
     public static function statementIf($condition = true, $returnIfTrue = 0, $returnIfFalse = false)
     {
+        if (Functions::isError($condition)) {
+            return $condition;
+        }
+
         $condition = ($condition === null) ? true : (bool) Functions::flattenSingleValue($condition);
         $returnIfTrue = ($returnIfTrue === null) ? 0 : Functions::flattenSingleValue($returnIfTrue);
         $returnIfFalse = ($returnIfFalse === null) ? false : Functions::flattenSingleValue($returnIfFalse);

tests/data/Calculation/Logical/IF.php

@@ -34,4 +34,10 @@
         'ABC',
         'XYZ',
     ],
+    [
+        '#N/A',
+        '#N/A',
+        'ABC',
+        'XYZ',
+    ],
 ];