I want to check the file name of Opportunity attachments using Groovy.

I want to generate an error when saving if there is an apostrophe in the file name of an Opportunity attachment.
When I implemented this in the BeforeUpdate trigger, if I changed items other than the attachment and saved, an error occurred if there was an apostrophe in the file name, but if I only inserted the attachment and saved, the error check did not occur.
Please tell me how to resolve this.