This Condition class executes a beanshell script and evaluates to true if
the script's last expression is either true (primitive or wrapper class)
or, for any other type, not null.
This class represents an operator which can be used in Conditions to evaluate the
operands specified in them.
It is defined abstract to allow different kinds of operators.
At the time of evaluation the concrete class of the operator has to provide a valid
Java expression by overriding
Operator.getExpression(String,String) .
This evaluates a condition related to one of the fields, or properties,
of the subject instance (passed in the
org.osbl.agent.model.RuleContext runtime-context ).