JsonVariant::isNull()
Description
JsonVariant::isNull() tests if the JsonVariant is unbound or points to a null value.
Remember that a JsonVariant is a reference to a value in a JsonDocument. A JsonVariant that is not attached to a JsonDocument will always be null:
JsonVariant variant;
variant.set(42); // does nothing because the variant is not attached to a document
variant.isNull(); // returns true
As an alternative, you can use the conversion to bool; for example, if(variant) instead of if(!variant.isNull())
Signature
bool isNull() const;
Return value
trueif theJsonVariantis unbound or points to anull.falseif theJsonVariantpoints to a non-null value.
Example
DynamicJsonDocument doc(1024);
deserializeJson("{\"a\":1,\"b\":null}");
doc["a"].isNull(); // false, because doc["a"] contains 1
doc["b"].isNull(); // true, because doc["b"] contains null
doc["c"].isNull(); // true, because doc["c"] doesn't exist
