@Override
  public String toString() {
    return "digest: " + digest + ", size: " + size;
  }
Checks if two {@link BlobDescriptor}s are equal.

<p>Two blobs are equal if their:

<ol>
  <li>{@code digest}s are not null and equal, and
  <li>{@code size}s are non-negative and equal
</ol>
jib-core/src/main/java/com/google/cloud/tools/jib/blob/BlobDescriptor.java