message: Add Default for StringValueLike
  Summary: Convenient to have.
diff: @@ -30,7 +30,10 @@ use serde::Serialize;
  use crate::{
  collections::{BorrowHashed, Hashed},
  - values::{string::StarlarkStr, Freeze, Freezer, FrozenValueTyped, Trace, ValueTyped},
  + values::{
  + layout::static_string::VALUE_EMPTY_STRING, string::StarlarkStr, Freeze, Freezer,
  + FrozenValueTyped, Trace, ValueTyped,
  + },
  };
  /// Convenient type alias.
  @@ -83,6 +86,18 @@ impl<'v> Equivalent<StringValue<'v>> for FrozenStringValue {
  }
  }
  +impl<'v> Default for StringValue<'v> {
  + fn default() -> Self {
  + FrozenStringValue::default().to_string_value()
  + }
  +}
  +
  +impl Default for FrozenStringValue {
  + fn default() -> Self {
  + VALUE_EMPTY_STRING.erase()
  + }
  +}
  +
  impl FrozenStringValue {
  /// Get self along with the hash.
  pub fn get_hashed(self) -> Hashed<Self> {
  @@ -126,6 +141,7 @@ pub trait StringValueLike<'v>:
  + CoerceKey<StringValue<'v>>
  + Display
  + Debug
  + + Default
  + Copy
  + Clone
  + Dupe
  