Using ConvertFrom-String with value that are not present in all sets of data

I have a text file with data that are structured (similarly to Json) that I want to parse with ConvertFrom-String to extract part of the data. I cannot change how the data are structured in the file so I have to deal with them the way they are.

Here's a sample of the data. The complete file has many more of these blocks and each block have more 'properties' than what I'm showing here (Keeping it small and readable :-) ). Note that the third block as a icon property that the other items don't have.

$Data = @'
    c_first_item = {    
        time = 270  
        category = cat_red
        min_value = {
            int = 10
        }
        max_value = {
            int = 20
        }
    }

    c_second_item = {   
        time = 270
        category = cat_blue
        min_value = {
            float = 10
        }
        max_value = {
            float = 20
        }
    }

    c_third_item = {    
        time = 270
        icon = c_third_icon
        category = cat_red
        min_value = {
            int = 10
        }
        max_value = {
            int = 20
        }
    }
'@

And here's my template used by ConvertFrom-String.

    $Template = @'
    {Name*:c_first_item} = \{   
        time = 270

        category = {Category:cat_red}


        random_property = \{
            random_property_value = 10
        \}

        random_property = \{
            random_property_value = 20
        \}
    \}

    {Name*:c_second_item} = \{
        time = 100
        icon = {Picture?:c_third_icon}

        category = {Category:cat_blue}

        random_property = \{
            random_property_value = 10
        \}

        random_property = \{
            random_property_value = 20
        \}
    \}
'@  

I was running this code with ConvertFrom-String to parse the data I wanted :

$Result = $Data | ConvertFrom-String -TemplateContent $Template

The expected result should have looked like this :

Name          Category  Picture
----          --------  -------
c_first_item  cat_red   
c_second_item cat_blue
c_third_item  cat_red   c_third_icon

But I was getting this instead :

Name          Category
----          --------
c_first_item  cat_red   
c_second_item cat_blue
c_third_item  cat_red  

As you can see there's no Picture property in my output object as ConvertFrom-String was unable to parse the data accordingly to what I asked. I guess the examples I'm giving aren't good enough to teach the algorythm how to react.

Is there a way for me to teach ConvertFrom-String to get an empty Picture property for the blocks where icon doesn't exists?

Update: 25th of January

As requested by @iRon, here's an example that adds a Length property to the result.

First, the file I'm parsing (Test.txt) :

d_mem_towers_sulfuric_forest = {
    is_for_colonizeable = yes
    category = deposit_cat_rare

    icon = d_radioactive_wasteland

    resources = {
        category = planet_deposits
        produces = {
            society_research = 4
            energy = 4
        }
    }

    planet_modifier = {
        planet_jobs_energy_produces_mult = 0.10
        planet_jobs_society_research_produces_mult = 0.10
        planet_max_districts_add = -1
        pop_environment_tolerance = -0.15
    }

    drop_weight = {
        weight = 0
    }
}

Then, the template file (Template.txt) :

{Object*:{Name:d_mem_sadrell_capital} = \{
    is_for_colonizeable = yes
    category = {Category:deposit_cat_rare}

    icon = {Picture:d_building}

    planet_modifier = \{
        planet_housing_add = 3
        pop_environment_tolerance = 0.1
        planet_jobs_specialist_produces_mult = 0.15
    \}

    triggered_planet_modifier = \{
        potential = \{
            exists = owner
            owner = \{ is_regular_empire = yes \}
        \}
        modifier = \{
            job_researcher_add = 2
            job_clerk_add = 2
        \}
    \}

    triggered_planet_modifier = \{
        potential = \{
            exists = owner
            owner = \{ is_hive_empire = yes \}
        \}
        modifier = \{
            job_brain_drone_add = 2
            job_maintenance_drone_add = 2
        \}
    \}

    triggered_planet_modifier = \{
        potential = \{
            exists = owner
            owner = \{ is_machine_empire = yes \}
        \}
        modifier = \{   
            job_calculator_add = 2
            job_maintenance_drone_add = 2
        \}
    \}

    drop_weight = \{
        weight = 0
    \}
\}}

{Object*:{Name:d_mem_sadrell_industrial_complex} = \{
    is_for_colonizeable = yes
    category = {Category:deposit_cat_rare}

    icon = {Picture:d_crater}

    planet_modifier = \{
        pop_environment_tolerance = -0.1
        planet_jobs_minerals_produces_mult = 0.25
        district_mining_max = 4
    \}

    drop_weight = \{
        weight = 0
    \}
\}}

{Object*:{Name:_mem_strange_mountain} = \{
    time = 365
    is_for_colonizeable = yes
    category = {Category:deposit_cat_blockers}

    icon = {Picture:d_mem_strange_mountain}

    resources = \{
        category = deposit_blockers
        cost = \{
            energy = 1000
            minerals = 1000
        \}
    \}

    drop_weight = \{
        weight = 0
    \}
\}}

Finally, here's the piece of code I'm using to extract the data :

$testText = Get-Content  -Path "Path\to\text.txt" #MEM
$template = 'Path\to\template.txt'

$result = $testText |
    ConvertFrom-String -TemplateFile $template |
    Select-Object -ExpandProperty Object |
    Union-Object

$result

The expected result should be like that :

Name                         Category         Picture               
----                         --------         -------        
d_mem_towers_sulfuric_forest deposit_cat_rare d_radioactive_wasteland

But I'm getting this instead :

Name                         Category         Picture                 Length
----                         --------         -------                 ------
d_mem_towers_sulfuric_forest deposit_cat_rare d_radioactive_wasteland
                                                                      0

There's a second line to my object that contains a Length property that I don't parse so I guess it somehow comes from Union-Object.

Any idea?