Variables from generated XML file of FreeOPCUA/opcua-modeler do not have set value types

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Problem

• (X) bug report => please search github for a similar issue or PR before submitting
• (X) unexpected behavior => please visit the Wiki before

Current behavior
A normal Server node with a node-set xml file loaded, created with the FreeOPCUA/opcua-modeler, does not allow for read write operations on the variables. In the modeler the value section under the variable-nodes attributes is present as expected. Connecting with the FreeOPCUA/opcua-client to the newly created server through the normal opcua-server node, the same variable now does not provide this 'Value' field. Thus, when trying to read/write to the variable it responds with the error "The access level does not allow writing to the Node."

Expected behavior
The XML file is interpreted correctly and provides the variables with read/write-able Value components.

Minimal reproduction of the problem with instructions

1. Download the FreeOpcUa/opcua-modeler
2. use the modeler to create a TestObject node and under that a variable TestDouble of type Double and value 0.0
3. use the saved XML-file in a fresh node-opcua server node under XML-Sets
4. download a client to verify like FreeOpcUa/opcua-client-gui)
5. use a client to connect to the server and open the TestDouble variable
6. try to read/write values to the TestDouble-variable

Following already created and used XML-contents (skip step 1-2):

<?xml version='1.0' encoding='utf-8'?>
<UANodeSet xmlns="http://opcfoundation.org/UA/2011/03/UANodeSet.xsd" xmlns:uax="http://opcfoundation.org/UA/2008/02/Types.xsd" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <NamespaceUris />
  <Aliases>
    <Alias Alias="Double">i=11</Alias>
    <Alias Alias="Organizes">i=35</Alias>
    <Alias Alias="HasTypeDefinition">i=40</Alias>
    <Alias Alias="HasComponent">i=47</Alias>
  </Aliases>
  <UAObject BrowseName="0:TestObject" NodeId="i=20001" ParentNodeId="i=85">
    <DisplayName>TestObject</DisplayName>
    <Description>The base type for all object nodes.</Description>
    <References>
      <Reference IsForward="false" ReferenceType="Organizes">i=85</Reference>
      <Reference ReferenceType="HasTypeDefinition">i=58</Reference>
      <Reference ReferenceType="HasComponent">i=20002</Reference>
    </References>
  </UAObject>
  <UAVariable BrowseName="0:TestDouble" DataType="Double" NodeId="i=20002" ParentNodeId="i=20001">
    <DisplayName>TestDouble</DisplayName>
    <Description>TestDouble</Description>
    <References>
      <Reference IsForward="false" ReferenceType="HasComponent">i=20001</Reference>
      <Reference ReferenceType="HasTypeDefinition">i=63</Reference>
    </References>
    <Value>
      <uax:Double>0.0</uax:Double>
    </Value>
  </UAVariable>
</UANodeSet>

Your Environment

Please tell us about your environment:

• (X) I am using just the Node-RED package and got node-opcua installed with it

• ( ) I have installed node-opcua global from source (using git clone)

• ( ) I have installed node-opcua as a global package (using npm i -g)

• Device (for Modelling):

  • ( ) macOS: v
  • (X) Linux: Linux 4.15.12-301.fc27.x86_64 Call OPC UA Methods with Array Input parameters #1 SMP x86_64 GNU/Linux
  • ( ) Windows: v
  • ( ) Raspbian: v
  • ( ) Other:
    • Name:
    • Version:

• Device (for Node-RED execution):

  • ( ) macOS: v
  • (X) Linux: Linux 3.4.113-sun8i BadIdentityTokenInvalid (0x80200000) using securityPolicy:Basic256 and securityMode:Sign #18 SMP PREEMPT armv7l GNU/Linux
  • ( ) Windows: v
  • ( ) Raspbian: v
  • ( ) Other:
    • Name:
    • Version:

• Description of the connecting OPC UA system:

  • Name: node-red-contrib-iiot-opcua read/write nodes (connector)
  • Version: 2.5.2
  • Vendor:
  • Link: https://

• node-red-contrib-iiot-opcu version: 2.5.2

• Node: (min. 8.x)
  node --version = 8.9.4

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