Update Troubleshooting.md and Gson default lenient mode documentation

Troubleshooting.md

@@ -129,7 +129,7 @@ Notes:
 
 **Solution:** See [`Gson` class documentation](https://www.javadoc.io/doc/com.google.code.gson/gson/latest/com.google.gson/com/google/gson/Gson.html) section "Lenient JSON handling"
 
-Note: Even in non-lenient mode Gson deviates slightly from the JSON specification, see [`JsonReader.setLenient`](https://www.javadoc.io/doc/com.google.code.gson/gson/latest/com.google.gson/com/google/gson/stream/JsonReader.html#setLenient(boolean)) for more details.
+Note: Even in non-lenient mode Gson deviates slightly from the JSON specification, see [`JsonReader.setStrictness`](https://www.javadoc.io/doc/com.google.code.gson/gson/latest/com.google.gson/com/google/gson/stream/JsonReader.html#setStrictness(Strictness)) for more details.
 
 ## `IllegalStateException`: "Expected ... but was ..."
 

gson/src/main/java/com/google/gson/Gson.java

@@ -106,12 +106,13 @@
  * for a more complete set of examples.</p>
  *
  * <h2>Lenient JSON handling</h2>
- * For legacy reasons most of the {@code Gson} methods allow JSON data which does not
+ * For legacy reasons most of the {@code Gson} methods by default allow JSON data which does not
  * comply with the JSON specification, even when the strictness {@link Strictness#DEFAULT}
  * is used. To restrict a {@code Gson} instance from parsing JSON that
- * does not comply with the JSON specification, {@linkplain Strictness#STRICT strict} mode should be used.
- * Alternatively, if you do not want to use {@linkplain Strictness#STRICT strict} mode,
- * the following workarounds can be used:
+ * does not comply with the JSON specification, {@link Strictness#STRICT} mode should be used.
+ *
+ * <p>For older Gson versions which don't have the {@link Strictness} mode API the following
+ * workarounds can be used:
  *
  * <h3>Serialization</h3>
  * <ol>