@CanIgnoreReturnValue
      public Entry makePrimary() {
        if (builder != null) {
          builder.clearPrimary();
        }
        isPrimary = true;
        return this;
      }
Marks that this entry is the primary key.

<p>Other entries in the same keyset will be marked as non-primary if this Entry has already
been added to a builder, otherwise they will marked as non-primary once this entry is added
to a builder.
java_src/src/main/java/com/google/crypto/tink/KeysetHandle.java