code: public static Expression createExpressionForField(FieldExtension fieldExtension) {
          if (StringUtils.isNotEmpty(fieldExtension.getExpression())) {
              ExpressionManager expressionManager = Context.getProcessEngineConfiguration().getExpressionManager();
              return expressionManager.createExpression(fieldExtension.getExpression());
          } else {
              return new FixedValue(fieldExtension.getStringValue());
          }
      }
docs: Creates an {@link Expression} for the {@link FieldExtension}.