fix: Test case fixes and linting issues
diff --git a/erpnext/patches/v13_0/create_pan_field_for_india.py b/erpnext/patches/v13_0/create_pan_field_for_india.py
index e94a9d9..01d4305 100644
--- a/erpnext/patches/v13_0/create_pan_field_for_india.py
+++ b/erpnext/patches/v13_0/create_pan_field_for_india.py
@@ -1,4 +1,3 @@
-import frappe
 from frappe.custom.doctype.custom_field.custom_field import create_custom_fields
 
 
diff --git a/erpnext/regional/india/utils.py b/erpnext/regional/india/utils.py
index 0e41280..1733220 100644
--- a/erpnext/regional/india/utils.py
+++ b/erpnext/regional/india/utils.py
@@ -62,7 +62,7 @@
 				.format(doc.gst_state_number), title=_("Invalid GSTIN"))
 
 def validate_pan_for_india(doc, method):
-	if doc.get('country') != 'India' or not doc.pan:
+	if doc.get('country') != 'India' or not doc.get('pan'):
 		return
 
 	if not PAN_NUMBER_FORMAT.match(doc.pan):
diff --git a/erpnext/selling/doctype/customer/customer.json b/erpnext/selling/doctype/customer/customer.json
index fa6e932..ae40630 100644
--- a/erpnext/selling/doctype/customer/customer.json
+++ b/erpnext/selling/doctype/customer/customer.json
@@ -212,7 +212,8 @@
    "fieldtype": "Link",
    "ignore_user_permissions": 1,
    "label": "Represents Company",
-   "options": "Company"
+   "options": "Company",
+   "unique": 1
   },
   {
    "depends_on": "represents_company",