Do not use String as default value for property type mismatch

[mrckzgl]

Previous issue name: Error when adding a vertex propery with cardinality list by providing a value list (only providing a single value is possible)
Suggestion after finding the root cause: #3490

Initial issue description:

• Version: 0.6.1
• Storage Backend: berkleyje
• Mixed Index Backend: lucene
• Expected Behavior: No Error
• Current Behavior: Error
• Steps to Reproduce:

Consider this JRuby code, where "prop_test" does not yet exist in the schema:

  dbtx = DB
  traverser = dbtx.traversal.add_v()
  traverser.property(VertexProperty::Cardinality::list, "prop_test", ["test"])
  traverser.iterate()
  dbtx.tx().commit()

The expected result is to add a vertex property "prop_test" of cardinality list with values ["test"]. However I got following error:

2023-01-23 14:49:51 - Java::JavaLang::IllegalArgumentException - Property value [["test"]] is of type class org.jruby.specialized.RubyArrayOneObject is not supported:
	org.apache.tinkerpop.gremlin.structure.Property$Exceptions.dataTypeOfPropertyValueNotSupported(org/apache/tinkerpop/gremlin/structure/Property.java:159)
	org.apache.tinkerpop.gremlin.structure.Property$Exceptions.dataTypeOfPropertyValueNotSupported(org/apache/tinkerpop/gremlin/structure/Property.java:155)
	org.janusgraph.graphdb.transaction.StandardJanusGraphTx.verifyAttribute(org/janusgraph/graphdb/transaction/StandardJanusGraphTx.java:638)
	org.janusgraph.graphdb.transaction.StandardJanusGraphTx.addProperty(org/janusgraph/graphdb/transaction/StandardJanusGraphTx.java:853)
	org.janusgraph.graphdb.transaction.StandardJanusGraphTx.addProperty(org/janusgraph/graphdb/transaction/StandardJanusGraphTx.java:842)
	org.janusgraph.graphdb.vertices.AbstractVertex.property(org/janusgraph/graphdb/vertices/AbstractVertex.java:180)
	org.janusgraph.graphdb.vertices.AbstractVertex.property(org/janusgraph/graphdb/vertices/AbstractVertex.java:45)
	org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.AddPropertyStep.sideEffect(org/apache/tinkerpop/gremlin/process/traversal/step/sideEffect/AddPropertyStep.java:165)
	org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.SideEffectStep.processNextStart(org/apache/tinkerpop/gremlin/process/traversal/step/sideEffect/SideEffectStep.java:39)
	org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(org/apache/tinkerpop/gremlin/process/traversal/step/util/AbstractStep.java:150)
	org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(org/apache/tinkerpop/gremlin/process/traversal/step/util/ExpandableStepIterator.java:55)
	org.apache.tinkerpop.gremlin.process.traversal.step.filter.FilterStep.processNextStart(org/apache/tinkerpop/gremlin/process/traversal/step/filter/FilterStep.java:37)
	org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.next(org/apache/tinkerpop/gremlin/process/traversal/step/util/AbstractStep.java:135)
	org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.next(org/apache/tinkerpop/gremlin/process/traversal/step/util/AbstractStep.java:40)
	org.apache.tinkerpop.gremlin.process.traversal.Traversal.iterate(org/apache/tinkerpop/gremlin/process/traversal/Traversal.java:210)
	org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal.iterate(org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal.java:2994)
	org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal$Admin.iterate(org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal.java:192)
	org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.DefaultGraphTraversal.iterate(org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/DefaultGraphTraversal.java:48)

Interestingly, when additionally providing a single value for the first time defining the property like this:

  traverser = dbtx.traversal.add_v()
  traverser.property(VertexProperty::Cardinality::list, "prop_test", "test")
  traverser.property(VertexProperty::Cardinality::list, "prop_test", ["test"])
  traverser.iterate()
  dbtx.tx().commit()

It works without error and the property "prop_test" is created with cardinality list.

best

[mrckzgl]

Ok, see also #3479. It is not possible to provide a list through .property. If the property key does not yet exist the unsupported type error is thrown. If the key, however, already exists as in the second case, the lists' string representation (probably calling .toString under the hood) is added as value. This IMHO is bad design, as it will lead to hard to debug problems. Instead, also in the second case the error should be thrown.

[porunov]

I don't have strong opinion, but I guess this was created for convenience when using gremlin console.
What could be done I guess, it adding a new configuration property which will enforce strong value type requirement and throw an exception instead of calling toString() for String based properties.