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Method isProperName() is noncompliant because it may be called with a null argument, resulting in a null pointer dereference.

Compliant Solution (Wrapped Method)

This compliant solution includes the same isProperName() method implementation as the previous noncompliant example, but it is now a private method with only one caller in its containing class.  

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The calling method, testString(), guarantees that isProperName() is always called with a valid string reference.  As a result, the class conforms with this rule, even though a public isProperName() method would not. Guarantees of this sort can be used to eliminate null pointer dereferences.

Compliant Solution (Optional Type)

This compliant solution uses an Optional String instead of a String object that may be null. The Optional class ([API 2014] java.util.Optional) was introduced in Java 8 to make dealing with possibly null objects easier, see [Urma 2014].

public boolean isProperName(Optional<String> os) {
  if (os.isPresent()) {
    String names[] = os.get().split(" ");
    if (names.length != 2) {
      return false;
    }
    return (isCapitalized(names[0]) && isCapitalized(names[1]));
  else {
    return false;
  }
}

The Optional class contains methods that can be used in the functional style of Java 8 to make programs shorter and more intuitive, as illustrated in the technical note by Urma cited above.

Exceptions

EXP01-EX0: A method may dereference an object-typed parameter without guarantee that it is a valid object reference provided that the method documents that it (potentially) throws a NullPointerException, either via the throws clause of the method or in the method comments. However, this exception should be relied upon sparingly.

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