$split: return undefined for non-string input (RecoLabs#1)

The jsonata npm package returns undefined when $split receives a
non-string first argument (number, boolean, etc.), but gnata threw
a hard T0410 error. This divergence caused silent evaluation
mismatches when gnata was used as a drop-in replacement.

Return nil (undefined) instead of erroring, matching the reference
jsonata behavior. The nil-input path was already handled correctly.

Signed-off-by: NirBarak-RecoLabs <nirb@recolabs.ai>

Author: NirBarak-RecoLabs

functions/string_funcs.go

@@ -424,7 +424,7 @@ func fnSplit(args []any, _ any) (any, error) {
 	}
 	s, ok := args[0].(string)
 	if !ok {
-		return nil, &evaluator.JSONataError{Code: "T0410", Message: "$split: argument 1 must be a string"}
+		return nil, nil
 	}
 	if len(args) < 2 {
 		return nil, &evaluator.JSONataError{Code: "D3006", Message: "$split: requires at least 2 arguments"}

testdata/groups/function-split/case016.json

@@ -2,5 +2,5 @@
     "expr": "$split(12345, 3)",
     "dataset": null,
     "bindings": {},
-    "code": "T0410"
+    "undefinedResult": true
 }

testdata/groups/function-split/case017.json

@@ -2,5 +2,5 @@
     "expr": "$split(12345)",
     "dataset": null,
     "bindings": {},
-    "code": "T0410"
+    "undefinedResult": true
 }