Comparision directly on null value safe?

Question

So many times, we do a null check of a field value and then compare them

boolean checkAmountGreaterThan10k(Opportunity record){
    if(record.Amount!=null){
       return record.Amount > 10000;
    }
    return false;
}

Then I recently discovered that any comparison operation performed on null value returns false.

Something like :

Integer bla = null;
System.debug(bla > 10000);//Prints 'false'
System.debug(bla >= 10000);//Prints 'false'
System.debug(bla < 10000);//Prints 'false'
System.debug(bla <= 10000);//Prints 'false'

System.debug( bla + 10000); // throws Null Ptr Exception

Thus I was thinking to use this in the above checkAmountGreaterThan10k as

boolean checkAmountGreaterThan10k(Opportunity record){  
       return record.Amount > 10000;    
}

Is this a documented behavior of comparison operator involving null, I was thinking about saving many lines of code with this.

I came from java world where I used to check null every time, similar java equivalent code throws NullPtrException

class Ideone
{
    public static void main (String[] args) throws java.lang.Exception
    {
        System.out.println("Hello World");
        Integer i = null ;
        System.out.println(i < 20); //Exception in thread "main" java.lang.NullPointerException,
    }
}

Java code link:

Is the Apex Runtime not throwing a null ptr exception in Apex a bug or undocumented feature?

Answer 1

I find this behavior documented in the Apex Developer Guide's Expression Operators for the comparison operators:

• Less than operator
• Greater than operator
• Less than or equal to operator
• Greater than or equal to operator.

If x or y equal null and are Integers, Doubles, Dates, or Datetimes, the expression is false.

Answer 2

Surprisingly (to me), this behavior is documented. I have pasted the reference for <, but the same statement is made for <=, >, and >=.

Operator <

Syntax
x < y

Description
Less than operator. If x is less than y, the expression evaluates to true. Otherwise, the expression evaluates to false.
Note:

• Unlike other database stored procedures, Apex does not support tri-state Boolean logic, and the comparison of any two values can never result in null.
• If x or y equal null and are Integers, Doubles, Dates, or Datetimes, the expression is false.
• A non-null String or ID value is always greater than a null value.
• If x and y are IDs, they must reference the same type of object. Otherwise, a runtime error results.
• If x or y is an ID and the other value is a String, the String value is validated and treated as an ID.
• x and y cannot be Booleans.
• The comparison of two strings is performed according to the locale of the context user and is case-insensitive.

---

On the contrary, the following operators note

x and y cannot be null

• +=
• *=
• -=
• /=
• |=
• &=
• &&
• ||

Surprisingly, this indication is not made for arithmetic operations, even though it still holds.