Gets a environment variable, or falls back to a property

getConfigurationParameter.gradle

/**
 * Looks for the specified configuration key in this order:
 *
 * <ol>
 *     <li>system environment</li>
 *     <li>project properties</li>
 * </ol>
 *
 * If it isn't found, then the empty string is returned. This stops the gradlew from failing until
 * it actually needs those values.
 *
 * @param keyName The key to look for
 * @return The value or the empty string if not found
 */
def getConfigurationParameter(String keyName) {
    return System.getenv(keyName) ?:
            rootProject.hasProperty(keyName) ? rootProject.properties[keyName] : ''
}