Build a comparator:

Comparator<BigDecimal> c = Comparator.nullsFirst(Comparator.naturalOrder());

(Or nullsLast, it doesn't matter if you're only ever comparing to zero).

Then:

if (c.compare(first, second) != 0) {
  // ...
}

If your main goal is validating BigDecimal dataType for nulls, then just make a comparison;

yourBigDecimal != null.

The above statement is enough for comparison and checking.

Use compareTo(BigDecimal.ZERO) instead of equals():

if (price.compareTo(BigDecimal.ZERO) == 0) // see below

Comparing with the BigDecimal constant BigDecimal.ZERO avoids having to construct a new BigDecimal(0) every execution.

FYI, BigDecimal also has constants BigDecimal.ONE and BigDecimal.TEN for your convenience.

Note!

The reason you can't use BigDecimal#equals() is that it takes scale into consideration:

new BigDecimal("0").equals(BigDecimal.ZERO) // true
new BigDecimal("0.00").equals(BigDecimal.ZERO) // false!

so it's unsuitable for a purely numeric comparison. However, BigDecimal.compareTo() doesn't consider scale when comparing:

new BigDecimal("0").compareTo(BigDecimal.ZERO) == 0 // true
new BigDecimal("0.00").compareTo(BigDecimal.ZERO) == 0 // true

The NullPointerException is occurring because the REPL calls toString() after the val assignment, which throws the exception. This is why it's not throwing the exception using lazy evaluation, since it doesn't call toString() then.

scala.math.BigDecimal is a class that holds a java.math.BigDecimal, but an instance of scala.math.BigDecimal holding a null value isn't a null reference itself. In your example (y.bigDecimal == null) will evaluate to true.

In any case, Option was created for a reason, and it's a much better idea to use it instead of assigning and checking nulls.

Edit:

Doing something like this:

val x : java.math.BigDecimal = null
BigDecimal(x) == BigDecimal(x)

.. Will throw a NullPointerException because BigDecimal will inevitably call this:

def compare (that: BigDecimal): Int = this.bigDecimal compareTo that.bigDecimal

.. Which compares the wrapped java.math.BigDecimals, and compareTo throws the exception when it finds the null.