Remove error message on null template

[jpelgrom]

Summary

In #2653 it was discovered that templates can be valid and return null, and some simple changes were made to handle it.

This PR builds on it and addresses a comment by another user:

The app presents null as "Error in template".

IMO, that message is not correct given the template is syntactically valid and doesn't throw an exception: null is a perfectly valid, if not intended, result here. If I didn't know this now, I'd have been going over the template for syntax errors and ripping my hair out wondering why I couldn't find any; null would tell me that it's working, just not giving me the info I want. That said, this could've already been hashed out elsewhere and decided on already so I end my comments on it here.

null will now be shown as "null" like in the frontend, and "Error in template" will only be shown if there is actually an error. If users want to avoid seeing "null" it can be handled in the template.

Screenshots

n/a, template widget/tile hasn't visually changed

Link to pull request in Documentation repository

n/a

Any other notes

On error the server will give the app a response like this:

{"template": {"error": "TemplateSyntaxError: expected name or number"}}

Which throws:

A stacktrace

2022-07-30 21:28:26.642 32676-32715/io.homeassistant.companion.android.debug E/TemplateWidgetConfigAct: Exception while rendering template
    io.homeassistant.companion.android.common.data.integration.IntegrationException: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.lang.String` from Object value (token `JsonToken.START_OBJECT`)
        at [Source: (okhttp3.ResponseBody$BomAwareReader); line: 1, column: 14] (through reference chain: java.util.LinkedHashMap["template"])
        at io.homeassistant.companion.android.common.data.integration.impl.IntegrationRepositoryImpl.renderTemplate(IntegrationRepositoryImpl.kt:177)
        at io.homeassistant.companion.android.common.data.integration.impl.IntegrationRepositoryImpl$renderTemplate$1.invokeSuspend(Unknown Source:15)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:104)
        at kotlinx.coroutines.internal.LimitedDispatcher.run(LimitedDispatcher.kt:42)
        at kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:95)
        at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:570)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:750)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:677)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:664)
     Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.lang.String` from Object value (token `JsonToken.START_OBJECT`)
        at [Source: (okhttp3.ResponseBody$BomAwareReader); line: 1, column: 14] (through reference chain: java.util.LinkedHashMap["template"])
        at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1741)
        at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1515)
        at com.fasterxml.jackson.databind.DeserializationContext.handleUnexpectedToken(DeserializationContext.java:1420)
        at com.fasterxml.jackson.databind.DeserializationContext.extractScalarFromObject(DeserializationContext.java:932)
        at com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:62)
        at com.fasterxml.jackson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:11)
        at com.fasterxml.jackson.databind.deser.std.MapDeserializer._readAndBindStringKeyMap(MapDeserializer.java:609)
        at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:437)
        at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:32)
        at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:323)
        at com.fasterxml.jackson.databind.ObjectReader._bindAndClose(ObjectReader.java:2051)
        at com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:1459)
        at retrofit2.converter.jackson.JacksonResponseBodyConverter.convert(JacksonResponseBodyConverter.java:33)
        at retrofit2.converter.jackson.JacksonResponseBodyConverter.convert(JacksonResponseBodyConverter.java:23)
        at retrofit2.OkHttpCall.parseResponse(OkHttpCall.java:243)
        at retrofit2.OkHttpCall$1.onResponse(OkHttpCall.java:153)
        at okhttp3.internal.connection.RealCall$AsyncCall.run(RealCall.kt:519)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1137)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:637)
        at java.lang.Thread.run(Thread.java:1012)

[dshokouhi]

Looks good to me