[PHP] Accept 0 as value for query parameters (#13868)

samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php

@@ -157,6 +157,49 @@ class ObjectSerializer
         return rawurlencode(self::toString($value));
     }
 
+    /**
+     * Checks if a value is empty, based on its OpenAPI type.
+     *
+     * @param mixed  $value
+     * @param string $openApiType
+     *
+     * @return bool true if $value is empty
+     */
+    private static function isEmptyValue($value, string $openApiType): bool
+    {
+        # If empty() returns false, it is not empty regardless of its type.
+        if (!empty($value)) {
+            return false;
+        }
+
+        # Null is always empty, as we cannot send a real "null" value in a query parameter.
+        if ($value === null) {
+            return true;
+        }
+
+        switch ($openApiType) {
+            # For numeric values, false and '' are considered empty.
+            # This comparison is safe for floating point values, since the previous call to empty() will
+            # filter out values that don't match 0.
+            case 'int':
+            case 'integer':
+                return $value !== 0;
+
+            case 'number':
+            case 'float':
+                return $value !== 0 && $value !== 0.0;
+
+            # For boolean values, '' is considered empty
+            case 'bool':
+            case 'boolean':
+                return !in_array($value, [false, 0], true);
+
+            # For all the other types, any value at this point can be considered empty.
+            default:
+                return true;
+        }
+    }
+
     /**
      * Take query parameter properties and turn it into an array suitable for
      * native http_build_query or GuzzleHttp\Psr7\Query::build.
@@ -178,10 +221,12 @@ class ObjectSerializer
         bool $explode = true,
         bool $required = true
     ): array {
-        if (
-            empty($value)
-            && ($value !== false || $openApiType !== 'boolean') // if $value === false and $openApiType ==='boolean' it isn't empty
-        ) {
+
+        # Check if we should omit this parameter from the query. This should only happen when:
+        #  - Parameter is NOT required; AND
+        #  - its value is set to a value that is equivalent to "empty", depending on its OpenAPI type. For
+        #    example, 0 as "int" or "boolean" is NOT an empty value.
+        if (self::isEmptyValue($value, $openApiType)) {
             if ($required) {
                 return ["{$paramName}" => ''];
             } else {