No, is an array of parties the witnesses are optionals

Regarding the rationale behind specifying the types of contracts upfront:

Standardization: By defining types, you create a standardized way to categorize and interpret contracts within the Nostr protocol. This can make it easier for applications built on top of Nostr to understand and process different contract types.

Clarity: Specifying types can provide clarity to the parties involved. Knowing whether an agreement is a legally binding "Contract" versus a less formal "Agreement" or a specific "Covenant" can set clear expectations for all parties.

Filtering & Searching: If there are many contracts within the Nostr network, having predefined types can make filtering and searching more efficient. Users or applications can quickly find all "Covenants" or all "Agreements" without having to parse the content of every contract.

Extensibility: While the initial types are predefined, the system can be designed to be extensible, allowing for the addition of new types in the future as the needs of the community evolve.

However, there are also arguments against specifying types upfront:

Flexibility: Restricting to predefined types might limit the flexibility of the system. Some contracts might not fit neatly into one of the predefined categories.

Overhead: Introducing types adds an additional layer of complexity to the system. Every contract will need to be categorized, and disputes might arise over which category is appropriate.

Evolution: As the protocol and its use cases evolve, the initially defined types might become obsolete or insufficient, requiring updates or revisions to the NIP.

In the end, the decision to specify contract types upfront depends on the goals of the Nostr protocol and the needs of its user community. If the aim is to keep things simple and flexible, it might be better to avoid predefined types. If the goal is to provide structure and standardization, then defining types can be beneficial.