Why is MapStruct warning this is an unmapped property

I am employing mapstruct to map between my network and database data objects within my current Android project.

api 'org.mapstruct:mapstruct:1.5.2.Final'
kapt 'org.mapstruct:mapstruct-processor:1.5.2.Final'

my network data class resembles this

@Keep
@Serializable
data class Item(

    @SerialName("actionTested")
    val actionTested: String? = null,

    @SerialName("agonistAntagonist")
    val agonistAntagonist: String = "",

    @SerialName("cellOrigin")
    val cellOrigin: String? = null,

    @SerialName("cmmnt")
    val comment: String? = null,

    @SerialName("displayDose")
    val displayDose: String = "",

    @SerialName("displayValue")
    val displayValue: String = "",

    @SerialName("document")
    val document: Document = Document(),

    @SerialName("documentYear")
    val documentYear: Int = 0,

    @SerialName("dose")
    val dose: String = "",

    @SerialName("doseUnit")
    val doseUnit: String? = null,

    @SerialName("drug")
    val drug: String = "",

    @SerialName("errorType")
    val errorType: String? = null,

    @SerialName("errorValue")
    val errorValue: String? = null,

    @SerialName("experimentType")
    val experimentType: String? = null,

    @SerialName("hash")
    val hash: String = "",

    @SerialName("id")
    val id: String = "",

    @SerialName("isPrimaryTarget")
    val isPrimaryTarget: String? = null,

    @SerialName("mutationDetail")
    val mutationDetail: String? = null,

    @SerialName("otherExpDetails")
    val otherExpDetails: String? = null,

    @SerialName("parameter")
    val parameter: String = "",

    @SerialName("sharpN")
    val sharpN: String? = null,

    @SerialName("smiles")
    val smiles: String? = null,

    @SerialName("source")
    val source: String = "",

    @SerialName("specie")
    val specie: String = "",

    @SerialName("strainRace")
    val strainRace: String? = null,

    @SerialName("studyType")
    val studyType: String = "",

    @SerialName("target")
    val target: String = "",

    @SerialName("targetType")
    val targetType: String = "",

    @SerialName("testSystem")
    val testSystem: String = "",

    @SerialName("transfection")
    val transfection: String = "",

    @SerialName("unitNormalized")
    val unitNormalized: String? = null,

    @SerialName("unitOriginal")
    val unitOriginal: String? = null,

    @SerialName("valueNormalized")
    val valueNormalized: String = "",

    @SerialName("valueOriginal")
    val valueOriginal: String = ""
)

My database data object resembles this

data class ActivitySearchItemDO(

    @ColumnInfo(name = "action_tested") val actionTested: String?,
    @ColumnInfo(name = "agonist_antagonist") val agonistAntagonist: String,
    @ColumnInfo(name = "cell_origin") val cellOrigin: String?,
    @ColumnInfo(name = "comment") val comment: String?,
    @ColumnInfo(name = "display_dose") val displayDose: String,
    @ColumnInfo(name = "display_value") val displayValue: String,
    @ColumnInfo(name = "document") val document: DocumentVO,
    @ColumnInfo(name = "document_year") val documentYear: Int,
    @ColumnInfo(name = "dose") val dose: String,
    @ColumnInfo(name = "dose_unit") val doseUnit: String?,
    @ColumnInfo(name = "drug") val drug: String,
    @ColumnInfo(name = "error_type") val errorType: String?,
    @ColumnInfo(name = "error_value") val errorValue: String?,
    @ColumnInfo(name = "experiment_type") val experimentType: String?,
    @ColumnInfo(name = "hash") val hash: String,
    @ColumnInfo(name = "id") val id: String,
    @ColumnInfo(name = "is_primary_target") val isPrimaryTarget: String? = null,
    @ColumnInfo(name = "mutation_detail") val mutationDetail: String?,
    @ColumnInfo(name = "other_exp_details") val otherExpDetails: String?,
    @ColumnInfo(name = "parameter") val parameter: String,
    @ColumnInfo(name = "sharp_N") val sharpN: String?,
    @ColumnInfo(name = "smiles") val smiles: String?,
    @ColumnInfo(name = "source") val source: String,
    @ColumnInfo(name = "specie") val specie: String,
    @ColumnInfo(name = "strain_race") val strainRace: String?,
    @ColumnInfo(name = "study_type") val studyType: String,
    @ColumnInfo(name = "target") val target: String,
    @ColumnInfo(name = "target_type") val targetType: String,
    @ColumnInfo(name = "test_system") val testSystem: String,
    @ColumnInfo(name = "transfection") val transfection: String,
    @ColumnInfo(name = "unit_normalized") val unitNormalized: String?,
    @ColumnInfo(name = "unit_original") val unitOriginal: String?,
    @ColumnInfo(name = "value_normalized") val valueNormalized: String,
    @ColumnInfo(name = "value_original") val valueOriginal: String
)

when i build my project i get the following warning and do not understand why

warning: Unmapped target property: "isPrimaryTarget".
    public abstract com.myapp.model.database.ActivitySearchItemDO map(@org.jetbrains.annotations.NotNull()

my mapper resembles this

@InheritInverseConfiguration(name = "map")
fun map(dataFields: Item): ActivitySearchItemDO

why is mapstruct reporting that the isPrimaryTarget is not being mapped?

UPDATE

it appears to be the "is" prefix that is causing the issue, when i remove is from the variable names it maps ok. which i am happy with as this field is not a boolean type but a String.

however i now have another case that is boolean and its generating a similar warning. why does mapstruct have an issue when mapping boolean fields.