fix required field check not accepting 0 and false values

Author: Jake Maldonado

src/classes/Entity.ts

@@ -1110,7 +1110,7 @@ class Entity<
 
     // Check for required fields
     Object.keys(required).forEach(field => 
-      required[field] !== undefined && !data[field] 
+      required[field] !== undefined && data[field] !== null
         && error(`'${field}${this.schema.attributes[field].alias ? `/${this.schema.attributes[field].alias}` : ''}' is a required field`)
     ) // end required field check