For workspace/symbol the spec defines WorkspaceSymbolParams as:

/**
 * The parameters of a Workspace Symbol Request.
 */
interface WorkspaceSymbolParams {
	/**
	 * A non-empty query string
	 */
	query: string;
}

The definition doesn't permit null or undefined and the comment says it's non-empty, however the language client sends requests with empty strings for the query when opening the workspace symbol list:

I'm raising this here since it seems to violate the spec, however I wonder if the spec should permit either null, undefined or "" since right now it seems like you couldn't list all.