Types of Errors in Salesforce (With Real Interview Scenarios)

Types of Errors in Salesforce (Quick Recap)

Apex Errors

• Compile-time errors
• Run-time errors (Exceptions)
• Logical errors

System Errors

• Governor limit errors
• CPU timeout
• Heap size exceeded
• Internal platform errors

LWC Errors

• JavaScript errors
• Template (HTML) errors
• Apex call errors
• Browser / runtime errors

Scenario 1: NullPointerException in Apex

Interview Question:

You are getting a NullPointerException in Apex. What could be the reasons and how do you fix it?

Answer: A NullPointerException occurs when we try to access an object or field that is not initialized.

Common causes:

• SOQL query returning no records
• Uninitialized sObject or list
• Accessing relationship fields without checking null

Solution:

• Always check for null
• Check list size before accessing

List<Account> accList = [SELECT Id, Name FROM Account WHERE Name = 'Test']; if(!accList.isEmpty()) { System.debug(accList[0].Name); }

Interview Tip:

“NullPointerException is the most common Apex runtime error in real projects.”

Scenario 2: Governor Limit – Too Many SOQL Queries

Interview Question:

Your code fails with Too many SOQL queries: 101. What went wrong?

Answer: This happens when SOQL queries are written inside loops, violating governor limits.

Bad Code:

for(Account acc : accList){ Contact c = [SELECT Id FROM Contact WHERE AccountId = :acc.Id]; }

Optimized Code:

List<Contact> conList = [SELECT Id, AccountId FROM Contact WHERE AccountId IN :accIds];

Interview Tip: “Bulkification is mandatory to avoid system limit exceptions.”

Scenario 3: DML Exception During Insert

Interview Question:

Insert operation fails with DmlException. How do you handle it?

Answer: DML exceptions occur due to:

• Validation rules
• Required fields missing
• Duplicate rules
• Permission issues

Proper Handling:

try { insert acc; } catch (DmlException e) { System.debug(e.getDmlMessage(0)); }

Best Practice: Use partial success with Database.insert(records, false).

Scenario 4: CPU Time Limit Exceeded

Interview Question:

Your batch or trigger fails with CPU timeout. What do you do?

Answer: CPU timeout happens due to:

• Nested loops
• Heavy string operations
• Complex logic in triggers

Fixes:

• Reduce nested loops
• Move logic to async (Batch / Queueable)
• Optimize conditions

Interview Line:“CPU issues are logic problems, not data problems.”

Scenario 5: LWC – Apex Call Fails but Works in Anonymous Apex

Interview Question:

Apex works in anonymous window but fails when called from LWC. Why?

Answer: Possible reasons:

• Missing @AuraEnabled
• Method not static
• Permission / FLS issues
• Exception thrown but not handled

Correct Method:

@AuraEnabled(cacheable=true) public static List<Account> getAccounts() { return [SELECT Id, Name FROM Account]; }

Scenario 6: LWC JavaScript Error – Undefined Property

Interview Question:

UI breaks with “Cannot read properties of undefined”. Why?

Answer: This happens when JS tries to access data before Apex response arrives.

Fix:

if(this.account && this.account.Name){ console.log(this.account.Name); }

Interview Tip: “Always assume async data may be undefined initially.”

Scenario 7: LWC Template Error – Missing Key

Interview Question:

Why is key mandatory in for:each?

Answer: key helps Salesforce track DOM elements efficiently. Without it, rendering issues occur.

<template for:each={list} for:item="item"> <div key={item.Id}>{item.Name}</div> </template>

Scenario 8: System Error – Internal Salesforce Error

Interview Question:

What do you do if you get an internal Salesforce error?

Answer:

• Capture debug logs
• Retry operation
• Raise Salesforce support ticket

Important: Internal errors are platform-level, not code issues.