Java tracesSampler callback allows returning null (#12499)

Author: adinauer

platform-includes/performance/sampling-function-intro/android.mdx

@@ -1,3 +1,3 @@
-To use the sampling function, set the <PlatformIdentifier name="traces-sampler" /> option in your `SentryAndroid.init()` to a function that will accept a <PlatformIdentifier name="sampling-context" /> dictionary and return a sample rate between 0 and 1. For example:
+To use the sampling function, set the <PlatformIdentifier name="traces-sampler" /> option in your `SentryAndroid.init()` to a function that will accept a <PlatformIdentifier name="sampling-context" /> dictionary and return a sample rate between 0 and 1. You should return the parent sampling decision if there is one. You may also return `null` and let the Java SDK make the decision as if no <PlatformIdentifier name="traces-sampler" /> was set. For example:
 
 <PlatformContent includePath="performance/traces-sampler-as-sampler" />

platform-includes/performance/sampling-function-intro/java.mdx

@@ -1,3 +1,3 @@
-To use the sampling function, set the <PlatformIdentifier name="traces-sampler" /> option in your `Sentry.init()` to a function that will accept a <PlatformIdentifier name="sampling-context" /> dictionary and return a sample rate between 0 and 1. For example:
+To use the sampling function, set the <PlatformIdentifier name="traces-sampler" /> option in your `Sentry.init()` to a function that will accept a <PlatformIdentifier name="sampling-context" /> dictionary and return a sample rate between 0 and 1. You should return the parent sampling decision if there is one. You may also return `null` and let the Java SDK make the decision as if no <PlatformIdentifier name="traces-sampler" /> was set. For example:
 
 <PlatformContent includePath="performance/traces-sampler-as-sampler" />

platform-includes/performance/traces-sampler-as-sampler/android.mdx

@@ -25,10 +25,10 @@ SentryAndroid.init(this, options -> {
         return 0.0;
       } else {
         // Default sample rate
-        return 0.1;
+        return null;
       }
     } else {
-      return 0.1;
+      return null;
     }
   });
 });
@@ -61,11 +61,11 @@ SentryAndroid.init(this) { options ->
         }
         else -> {
           // Default sample rate
-          0.1
+          null
         }
       }
     } else {
-      0.1
+      null
     }
   }
 }

platform-includes/performance/traces-sampler-as-sampler/java.mdx

@@ -26,10 +26,10 @@ Sentry.init(options -> {
         return 0.0;
       } else {
         // Default sample rate
-        return 0.1;
+        return null;
       }
     } else {
-      return 0.1;
+      return null;
     }
   });
 });
@@ -62,11 +62,11 @@ Sentry.init { options ->
         }
         else -> {
           // Default sample rate
-          0.1
+          null
         }
       }
     } else {
-      0.1
+      null
     }
   }
 }