Gradle Plugin: Calling apollo.customTypeMapping.put does nothing

[ansman]

Summary
Calling customTypeMapping.put without first calling set is ignored.

Version
2.4.6 (Gradle 6.7.1)

Description
To my surprise Gradle seems to ignore calls such as MapProperty.put if the property is not present. Here's some concrete examples:

apollo {
  // Prints `null`
  println(customTypeMapping.orNull)

  customTypeMapping.put("foo", "bar")
  // Prints `null`
  println(customTypeMapping.orNull)

  customTypeMapping.set(emptyMap())
  customTypeMapping.put("foo", "bar")
  // Prints `{foo=bar}`
  println(customTypeMapping.orNull)
}

The fix for this is simple, the Apollo Gradle Plugin just needs to set emptyMap() as the default value. Using convention does not work unfortunately.

The reason why I prefer put is because I often set up my Gradle scripts using custom Gradle plugins in buildSrc which can add some common default values.

[ansman]

This seems related to gradle/gradle#7485

[martinbonnin]

Yup, this behaviour is super weird. Recent versions of Gradle have a MapProperty.convention() method that allows to set a default value and distinguish between empty vs unset. Tentative fix there: #2803