Gradle 2.13 added a new method to get a property value: findProperty. This method will return a property value if the property exists or null if the property cannot be found. Gradle also has the property method to return a property value, but this method will throw an exception if the property is missing. With the new findProperty method and the Groovy elvis operator (?:) we can try to get a property value and if not found return a default value.

In the following example we have a task that tries to print the value of the properties sampleOld and sampleNew. We use the findProperty for sampleNew and the property method for sampleOld:

// File: build.gradle
task resolveProperties ${project.hasProperty('sampleOld') ? project.property('sampleOld') : 'default value for sampleOld'}"
 println "sampleNew -> ${project.findProperty('sampleNew') ?: 'default value for sampleNew'}"
}

First run the task and not set the project properties sampleOld and sampleNew:

$ gradle -q resolveProperties
sampleOld -> default value for sampleOld
sampleNew -> default value for sampleNew
$

Next we use the -P command line option to set a value for the properties:

$ gradle -q -PsampleOld="Value sampleOld" -PsampleNew="Value sampleNew" resolveProperties
sampleOld -> Value sampleOld
sampleNew -> Value sampleNew
$

Written with Gradle 2.13.