Add null value support to BaseEmailDocument interface

- Update BaseEmailDocument to support `| null` for optional fields (cc, bcc, from, replyTo, text, etc.)
- Update BaseEmailTemplateDocument to support `| null` for optional fields
- Add explicit null checks in sendEmail processing to handle null values properly
- Update CUSTOM-TYPES.md documentation to reflect null value compatibility

Fixes type constraint error where customer Email types had `cc?: string[] | null`
but BaseEmailDocument only supported `cc?: string[]`.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/types/index.ts

@@ -2,38 +2,38 @@ import { Payload } from 'payload'
 import type { CollectionConfig, RichTextField } from 'payload'
 import { Transporter } from 'nodemailer'
 
-// Generic base interfaces that work with any ID type
+// Generic base interfaces that work with any ID type and null values
 export interface BaseEmailDocument {
   id: string | number
   template?: any
   to: string[]
-  cc?: string[]
-  bcc?: string[]
-  from?: string
-  replyTo?: string
+  cc?: string[] | null
+  bcc?: string[] | null
+  from?: string | null
+  replyTo?: string | null
   subject: string
   html: string
-  text?: string
-  variables?: Record<string, any>
-  scheduledAt?: string
-  sentAt?: string
-  status?: 'pending' | 'processing' | 'sent' | 'failed'
-  attempts?: number
-  lastAttemptAt?: string
-  error?: string
-  priority?: number
-  createdAt?: string
-  updatedAt?: string
+  text?: string | null
+  variables?: Record<string, any> | null
+  scheduledAt?: string | null
+  sentAt?: string | null
+  status?: 'pending' | 'processing' | 'sent' | 'failed' | null
+  attempts?: number | null
+  lastAttemptAt?: string | null
+  error?: string | null
+  priority?: number | null
+  createdAt?: string | null
+  updatedAt?: string | null
 }
 
 export interface BaseEmailTemplateDocument {
   id: string | number
   name: string
   slug: string
-  subject?: string
+  subject?: string | null
   content?: any
-  createdAt?: string
-  updatedAt?: string
+  createdAt?: string | null
+  updatedAt?: string | null
 }
 
 export type BaseEmail<TEmail extends BaseEmailDocument = BaseEmailDocument, TEmailTemplate extends BaseEmailTemplateDocument = BaseEmailTemplateDocument> = Omit<TEmail, 'id' | 'template'> & {template: Omit<TEmailTemplate, 'id'> | TEmailTemplate['id'] | undefined | null}