Ensure find_vm returns nil when pool configuration or datacenter cann…

…ot be found. Document expected return values. Remove underscore preface from pool_name where the variable is used.

lib/vmpooler/providers/vsphere.rb

@@ -161,11 +161,11 @@ def vm_in_target?(pool_name, parent_host, architecture, target)
           return false
         end
 
-        def get_vm(_pool_name, vm_name)
+        def get_vm(pool_name, vm_name)
           vm_hash = nil
           @connection_pool.with_metrics do |pool_object|
             connection = ensured_vsphere_connection(pool_object)
-            vm_object = find_vm(_pool_name, vm_name, connection)
+            vm_object = find_vm(pool_name, vm_name, connection)
             return vm_hash if vm_object.nil?
 
             vm_folder_path = get_vm_folder_path(vm_object)
@@ -324,10 +324,10 @@ def revert_snapshot(pool_name, vm_name, snapshot_name)
           true
         end
 
-        def destroy_vm(_pool_name, vm_name)
+        def destroy_vm(pool_name, vm_name)
           @connection_pool.with_metrics do |pool_object|
             connection = ensured_vsphere_connection(pool_object)
-            vm_object = find_vm(_pool_name, vm_name, connection)
+            vm_object = find_vm(pool_name, vm_name, connection)
             # If a VM doesn't exist then it is effectively deleted
             return true if vm_object.nil?
 
@@ -793,9 +793,14 @@ def build_propSpecs(datacenter, folder, vmname)
         end
 
         def find_vm(pool_name, vmname, connection)
+          # Find a VM by its inventory path and return the VM object
+          # Returns nil when a VM, or pool configuration, cannot be found
           pool_configuration = pool_config(pool_name)
+          return nil if pool_configuration.nil?
           folder = pool_configuration['folder']
           datacenter = get_target_datacenter_from_config(pool_name)
+          return nil if datacenter.nil?
+
           propSpecs = {
             :entity => self,
             :inventoryPath => "#{datacenter}/vm/#{folder}/#{vmname}"