Weird Compilation Error while generating docs for class with scala-logging

[saveveltri]

Hello,

I'm encountering this strange behaviour while executing sbt unidoc in a module of my project which has got simple ADTs and only com.typesafe.scala-logging" %% "scala-logging" % "3.7.2 as a dependency.

Here is an example

sealed trait Statement {
  def db: String
}

case class SelectStatement(override val db: String)
    extends SQLStatement
    with LazyLogging {

  private def filterToExpression(dimension: String, operator: String, value:String): Option[Expression] = {
    operator match {
      case ">"         => Some(ComparisonExpression(dimension, GreaterThanOperator, value))
      case ">="        => Some(ComparisonExpression(dimension, GreaterOrEqualToOperator, value))
      case "="         => Some(EqualityExpression(dimension, value))
      case "<="        => Some(ComparisonExpression(dimension, LessOrEqualToOperator, value))
      case "<"         => Some(ComparisonExpression(dimension, LessThanOperator, value))
      case op @ _      =>
        logger.warn("Ignored filter with invalid operator: {}", op)
        None
    }
  }

scala version is 2.12.4

The exception got is

[error] 
[error]   last tree to typer: Ident(op)
[error]               symbol: value op (flags: <triedcooking>)
[error]    symbol definition: val op: String
[error]                  tpe: String
[error]        symbol owners: value op -> method filterToExpression -> class SelectSQLStatement -> package statement
[error]       context owners: method filterToExpression -> class SelectSQLStatement -> package statement
[error] 
[error] == Enclosing template or block ==
[error] 
[error] Block(
[error]   Apply(
[error]     "logger"."warn"
[error]     // 2 arguments
[error]     "Ignored filter with invalid operator: {}"
[error]     "op" // val op: String, tree.tpe=String
[error]   )
[error]   "None"
[error] )
[error] 
[error] == Expanded type of tree ==
[error] 
[error] TypeRef(
[error]   TypeSymbol(
[error]     final class String extends Serializable with Comparable[String] with CharSequence
[error]     
[error]   )
[error] )
[error] 
[error] uncaught exception during compilation: scala.MatchError

Honestly, I have no clue of what can cause such a low level exception.
Any hint or suggestion is much apprecciated.

Thanks for the support,
Saverio