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I want to implement kind of a proxy for some boolean values in my app. The logic would be as follows:

The question is - how can I check if the value exists in Firebase Remote Config?

I found another way, maybe useful for someone else landing here:

val rawValue = remoteConfig.getValue(key)
val exists = rawValue.source == FirebaseRemoteConfig.VALUE_SOURCE_REMOTE
In this case exists will be true only if the value is returned from remote (and and has not been set as default or static provided value). The accepted answer is error prone as does not consider the case where the empty String is a valid String returned from remote
Here the docs for FirebaseRemoteConfigValue 
                This is the correct answer. For C#: bool exists = rawValue.source == ValueSource.RemoteValue; Documentation here: firebase.google.com/docs/reference/unity/namespace/firebase/…
– DoomGoober
                Oct 29, 2020 at 2:49
I have found the solution:
Firebase Remote Config fetches ALL values as Strings and only then maps them to other types in convenience methods such as getBoolean(), getLong() etc.
Therefore, a boolean config value existence can be checked as follows:
String value = firebaseRemoteConfig.getString("someKey");
if(value.equals("true")){
    //The value exists and the value is true
} else if(value.equals("false")) {
    //The value exists and the value is false
} else if(value.equals("")) {
    //The value is not set in Firebase
Same goes for other types, i.e. a long value set to 64 on firebase will be returned from getString() as "64".
                Note that this is only valid if no default values are defined via setDefaultsAsync(). When you did define a default, getString() will return the default value.
– Martijn
                Jan 31, 2021 at 14:59
Firebase Remote Config (FRC), actually provides 3 constants to know from where is the value retrieved with getValue(forKey) (documentation)
VALUE_SOURCE_DEFAULT --> value from default set by user
VALUE_SOURCE_REMOTE --> value from remote server
VALUE_SOURCE_STATIC --> value returned is default (FRC don't have the key)
Knowing this, you can do a "wrapper" like this:
class FirebaseRemoteConfigManager {
.....
    override fun getBoolean(forKey: String): Boolean? = getRawValue(forKey)?.asBoolean()
    override fun getString(forKey: String): String? = getRawValue(forKey)?.asString()
    override fun getDouble(forKey: String): Double? = getRawValue(forKey)?.asDouble()
    override fun getLong(forKey: String): Long? = getRawValue(forKey)?.asLong()
    private fun getRawValue(forKey: String): FirebaseRemoteConfigValue? {
        val rawValue = remoteConfig.getValue(forKey)
        return if (rawValue.source == FirebaseRemoteConfig.VALUE_SOURCE_STATIC) null else rawValue
If you get a null, you know the key don't exist in FRC.
Take care of using default values as "not exist", because maybe in your FRC you want to set this value, and you will have a false positive
Remote Config already does this, as described in the documentation.  You're obliged to provide default values for parameters that haven't been defined in the console.  They work exactly as you describe, without having to do any extra work.  These defaults will be used until you perform a fetch.  If the value is defined in the console, then it will be used instead of the default.
                The problem is, the values would be dynamic. I want to be able to add a firebase proxy value without redeploying the app. Also, there is no obligation to define defaults from what I have seen. It just returns the default value for that data type (false, "" or 0)
– Kelevandos
                Dec 15, 2017 at 16:27
                These firebase values are supposed to be master values. So if there is one in firebase, use that. If not, use the one retrieved from the backend. And I want to be able to iterate all back-end values, check if there is an override in firebase and use that if so.
– Kelevandos
                Dec 15, 2017 at 17:09
                I don't think you're going to be able to know if a parameter has a value in the console unless you place a special value there that indicates to the app not to use it.
– Doug Stevenson
                Dec 15, 2017 at 17:17
        
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