System.JSONException: N/A

Question

When deserializing a JSON-serialized Apex object, received from a Lightning component, I'm getting the following error:

FATAL_ERROR System.JSONException: N/A at [line:1, column:155]

Data class:

global class SomeClass {
    @AuraEnabled
    global Decimal someField { get; set; }
}

Server-side Lightning controller:

@AuraEnabled
global static void someMethod(String objJson) {
    System.debug(objJson); // {"someField":""}
    SomeClass obj = (SomeClass)JSON.deserialize(objJson, SomeClass.class); // throws exception
}

Client-side Lightning controller:

"callServer" : function(component) {
    var obj = component.get("v.obj");
    obj.someField = valueFromInput; // an HTML input element

    var serverAction = component.get("c.someMethod");
    serverAction.setParams({ "objJson" : JSON.stringify(obj) });
    $A.enqueueAction(serverAction);
}

Answer 1

String values for numeric fields cause this error—even empty strings!

It's easy to make this mistake when grabbing the value from an HTML input in Lightning. The value of an empty input is the empty string, not null or undefined. If the value should be deserialized into a numeric data type, you must make sure to do validation not just for illegal non-empty values, but for empty values too.

// example just to illustrate the point
var validatedValue = valueFromInput !== "" ? valueFromInput : null;
obj.someField = validatedValue;

That said, the Salesforce error message is quite useless. Type mismatch should be pretty easy to report.