Which two of the following statements are true of embeddable classes? (Choose two)
A.
An embeddable class must not be used to represent the state of another embeddable class.
B.
Null comparison operations over embeddable classes are not supported in the Java
Persistence query language.
C.
An embeddable class must not contain a relationship to an entity.
D.
An embeddable class can be the key of a Map relationship.
Answer B , D
JPQL Null Comparison Expressions
The syntax for the use of the comparison operator IS NULL in a conditional expression is as
follows:
null_comparison_expression ::= {single_valued_path_expression | input_parameter } IS [NOT] NULL
A null comparison expression tests whether or not the single-valued path expression or input parameter is a NULL value.
Null comparisons over instances of embeddable class types are not supported.
check also this link :
http://openjpa.apache.org/builds/2.3.0/apache-openjpa/docs/jpa_langref.html