Why is Groovy evaluator returning NULL?

Question

I have the following code:

Binding binding = new Binding();
binding.setVariable("story", storyFactory.newStory());
GroovyShell shell = new GroovyShell(binding);
exp = getExpression();
System.out.println("Expression: " + exp);
Object result = (Object)shell.evaluate(exp);    

That produces the following NullPointerException and console output:

Expression: story.getDescriptions().get(0).setText(story.getDescriptions().get(0).getText().replace("@", "at").replace("\"", "'").replace("%", "percent"));
java.lang.NullPointerException
    at com.me.myapp.GroovyEvaluator._evaluate(GroovyEvaluator.java:56)
    at com.me.myapp.testing.expressions.Driver.runEvaluator(Driver.java:131)
    at com.me.myapp.testing.expressions.Driver.run(Driver.java:65)
    at com.me.myapp.testing.expressions.Driver.main(Driver.java:31)

null

Why is result NULL? It can't be a problem with the story instance, as I have verified in other code that getDescriptions() and getDescriptions().get(0) both return non-null values. Also, getDescriptions().get(0) does return a non-null, non-empty String value. Thanks in advance!

Answer 1

It returns the value of:

story.getDescriptions().get(0).setText

I assume setText has a void return type

Therefore you get null

Try changing your expression to:

story.descriptions.get( 0 ).with { d ->
    d.text = d.text.replace("@", "at")
                   .replace( '"', "'")
                   .replace( "%", "percent" )
    d
}

(or all on one line like):

story.descriptions.get( 0 ).with { d -> d.text = d.text.replace("@", "at").replace( '"', "'").replace( "%", "percent" ) ; d }