Fixing issue with rxjava2/3 based Promise implementations not handling null (#13972)

* fixing issue with rxjava based promise implementations not handling a  void/null promise return time

* cleaning up test comments

Author: davydotcom

grails-async/rxjava2/src/main/groovy/org/grails/async/factory/rxjava2/RxPromise.groovy

@@ -41,9 +41,10 @@ class RxPromise<T>  implements Promise<T> {
     protected boolean finished = false
 
     RxPromise(RxPromiseFactory promiseFactory, Closure callable, Scheduler scheduler) {
+
         this(promiseFactory, Single.create( { SingleEmitter<? super T> singleSubscriber ->
             try {
-                singleSubscriber.onSuccess((T)callable.call())
+                singleSubscriber.onSuccess((T)runCallable(callable))
             } catch (Throwable t) {
                 singleSubscriber.onError(t)
             }
@@ -158,4 +159,13 @@ class RxPromise<T>  implements Promise<T> {
             }
         }
     }
+
+    static Object runCallable(Closure callable) {
+        Object rtn = callable.call()
+        if(rtn == null) {
+            return Void
+        } else {
+            return rtn
+        }
+    }
 }

grails-async/rxjava2/src/test/groovy/org/grails/async/factory/rxjava2/RxPromiseSpec.groovy

@@ -54,6 +54,18 @@ class RxPromiseSpec extends Specification {
             result == [one: 1, two: 2, four: 4]
     }
 
+    void 'Test promise null handling'() {
+
+        when: 'a null promise result is created'
+        def promise = Promises.createPromise {
+            return null
+        }
+        def result = promise.get()
+
+        then: 'result is void'
+        result == Void
+    }
+
     void 'Test promise list handling'() {
 
         when: 'a promise list is created from two promises'

grails-async/rxjava3/src/main/groovy/org/grails/async/factory/rxjava3/RxPromise.groovy

@@ -41,7 +41,7 @@ class RxPromise<T>  implements Promise<T> {
     RxPromise(RxPromiseFactory promiseFactory, Closure callable, Scheduler scheduler) {
         this(promiseFactory, Single.create( { SingleEmitter<? super T> singleSubscriber ->
             try {
-                singleSubscriber.onSuccess((T)callable.call())
+                singleSubscriber.onSuccess((T)runCallable(callable))
             } catch (Throwable t) {
                 singleSubscriber.onError(t)
             }
@@ -156,4 +156,13 @@ class RxPromise<T>  implements Promise<T> {
             }
         }
     }
+
+    static Object runCallable(Closure callable) {
+        Object rtn = callable.call()
+        if(rtn == null) {
+            return Void
+        } else {
+            return rtn
+        }
+    }
 }

grails-async/rxjava3/src/test/groovy/org/grails/async/factory/rxjava3/RxPromiseSpec.groovy

@@ -41,6 +41,18 @@ class RxPromiseSpec extends Specification {
 
     }
 
+    void 'Test promise null handling'() {
+
+        when: 'a null promise result is created'
+        def promise = Promises.createPromise {
+            return null
+        }
+        def result = promise.get()
+
+        then: 'result is void'
+        result == Void
+    }
+
     void 'Test promise map handling'() {
 
         when: 'a promise map is created'