Fix multipleOf bugs in Number type

Fixes the multipleOf validation crashing when trying to use the modulo operator on a value that is zero, and an InvalidArgumentException when calling multipleOf() with `null` to reset it

Author: bertramakers

src/Schema/Type/Number.php

@@ -50,7 +50,7 @@ public function validate(mixed $value, callable $fail): void
             }
         }
 
-        if ($this->multipleOf !== null && $value % $this->multipleOf !== 0) {
+        if ($this->multipleOf !== null && (float) $value !== 0.0 && $value % $this->multipleOf !== 0) {
             $fail(sprintf('must be a multiple of %d', $this->multipleOf));
         }
     }
@@ -85,7 +85,7 @@ public function maximum(?float $maximum, bool $exclusive = false): static
 
     public function multipleOf(?float $number): static
     {
-        if ($number <= 0) {
+        if ($number !== null && $number <= 0) {
             throw new InvalidArgumentException('multipleOf must be a positive number');
         }