Fix IF implementation to comply with Excel behavior

Closes #1165

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 ### Fixed
 
+- IF implementation properly handles the value `#N/A` [#1165](https://github.com/PHPOffice/PhpSpreadsheet/pull/1165)
 - Formula Parser: Wrong line count for stuff like "MyOtherSheet!A:D" [#1215](https://github.com/PHPOffice/PhpSpreadsheet/issues/1215)
 - Call garbage collector after removing a column to prevent stale cached values
 - Trying to remove a column that doesn't exist deletes the latest column

src/PhpSpreadsheet/Calculation/Logical.php

@@ -266,6 +266,10 @@ class Logical
      */
     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 @@ return [
         'ABC',
         'XYZ',
     ],
+    [
+        '#N/A',
+        '#N/A',
+        'ABC',
+        'XYZ',
+    ],
 ];