src/Types/RepeatableType.php
public function offsetSet($offset, $value)
    {
        self::ensurePropertyType($value);

        if (is_null($offset)) {
            $this->data[] = $value;
        } else {
            $this->data[$offset] = $value;
        }
    }
public function offsetSet($offset, $value)
    {
        self::ensurePropertyType($value);

        if (is_null($offset)) {
            $this->data[] = $value;
        } else {
            $this->data[$offset] = $value;
        }
    }
Sets a value for the given offset.

@param mixed $offset The array index or null to add the value to the end of the array.
@param mixed $value The value to add.

@throws \DTS\eBaySDK\Exceptions\InvalidPropertyTypeException If the value is the wrong type for the array.