Unexpected null reference exception while trying to fetch the taskModel from executionDAOFacade

[amirpopovich]

Describe the bug

In method TaskModel getTaskModel(String taskId) within class ExecutionDAOFacade, if the call to getTaskFromDatastore(taskId) returns null, an unhandled exception will be thrown on the next line, when a call to populateTaskData(TaskModel taskModel) is made.

Details
Conductor version: 3.6.1
Persistence implementation: Dynomite
Queue implementation: Dynoqueues
Lock: Redis

Expected behavior
Check if the taskModel is null before calling populateTaskData as implemented in the method public Task getTask(String taskId).
This was the behavior in the past, until commit 3c74e0c45d710dc89b67ecdb6f3bbeeea27753a6 was made which did some changes without adding the null validation check.

Current Implementation

public TaskModel getTaskModel(String taskId) {
    TaskModel taskModel = getTaskFromDatastore(taskId);
    populateTaskData(taskModel);
    return taskModel;
}

Expected Implementation

 public TaskModel getTaskModel(String taskId) {
    TaskModel taskModel = getTaskFromDatastore(taskId);
    if(taskModel != null){
        populateTaskData(taskModel);
    }
    return taskModel;
}