better handling of null to convert to ''

Author: David Nahodyl

src/Database/Eloquent/FMModel.php

@@ -486,6 +486,11 @@ public function setAttribute($key, $value)
             $value = $value ? 1 : 0;
         }
 
+        // FileMaker can't handle null, so change it to ''
+        if (is_null($value)){
+            $value = '';
+        }
+
         $this->attributes[$key] = $value;
 
         return $this;