code: private void assertUnaryOperator(final String operator) {
      if (!("+".equals(operator) || "-".equals(operator) || "~".equals(operator))) {
        throw new JBBPCompilationException("Wrong unary operator '" + operator + "' [" + this.expressionSource + ']');
      }
    }
docs: Check that a string represents a unary operator.
  
  @param operator an operator to be checked, must not be null.
  @throws JBBPCompilationException if the operator is not supported unary operator.