Handle `sh:maxCount 0` in form fields

[dennisvang]

Description

Currently, fields with sh:maxCount 0 are rendered as "list" in the form.

For example, if we set sh:maxCount 0 in the default Catalog schema, the client (in this case v2.0.0-alpha.1) renders the following form:

Expected behavior

Definition of sh:maxCount from the SHACL spec:

If the number of value nodes is greater than $maxCount, there is a validation result.

This would imply that, for sh:maxCount 0, no value nodes are allowed at all.

Usage examples are found in the shacl-shacl shapes graph in the spec (in combination with sh:or). Also see e.g. validatingrdf.

Notes

Here's how the SHACL form renderer handles maxCount 0, based on isList():

FAIRDataPoint-client/src/components/ShaclForm/fieldUtils.ts

Lines 24 to 26 in d6eacb9

	function isList(field: FormField): boolean {
	return field.maxCount !== 1
	}

and in getShaclValue() we find:

FAIRDataPoint-client/src/utils/metadata.ts

Line 95 in d6eacb9

if (fieldConfig.maxCount === 1) {

Note that Field.maxCount (or FormField.maxCount) can be null:

FAIRDataPoint-client/src/components/ShaclForm/Parser/SHACLParser.ts

Line 61 in d6eacb9

maxCount: number | null