fix: Re-add Try-Catch for ConfigurationExceptions To DefaultPropertyP…

…laceholderResolver (#10798)

Fixes #10797 
* Adding try-catch for ConfigurationExceptions which are thrown when resolving env properties
* Adding test cases for placeholder resolution, both with and without the placeholder set
* Removing irrelevant print statement and method call to vehicle for the purposes of the specified unit tests

inject/src/main/java/io/micronaut/context/env/DefaultPropertyPlaceholderResolver.java

@@ -394,14 +394,18 @@ public <T> T getValue(Class<T> type) throws ConfigurationException {
 
         @Override
         public <T> Optional<T> findValue(Class<T> type) {
-            for (String expression: expressions) {
-                Optional<T> optionalValue = resolveOptionalExpression(expression, type);
-                if (optionalValue.isPresent()) {
-                    return optionalValue;
+            try {
+                for (String expression: expressions) {
+                    Optional<T> optionalValue = resolveOptionalExpression(expression, type);
+                    if (optionalValue.isPresent()) {
+                        return optionalValue;
+                    }
                 }
-            }
-            if (defaultValue != null) {
-                return conversionService.convert(defaultValue, type);
+                if (defaultValue != null) {
+                    return conversionService.convert(defaultValue, type);
+                }
+            } catch (ConfigurationException e) {
+                // Swallow exception.
             }
             return Optional.empty();
         }

test-suite/src/test/java/io/micronaut/docs/config/value/Engine.java

@@ -19,4 +19,6 @@ public interface Engine {
     int getCylinders();
 
     String start();
+
+    String getDescription();
 }

test-suite/src/test/java/io/micronaut/docs/config/value/EngineImpl.java

@@ -17,6 +17,7 @@
 
 // tag::imports[]
 import io.micronaut.context.annotation.Value;
+import io.micronaut.core.annotation.Nullable;
 
 import jakarta.inject.Singleton;
 // end::imports[]
@@ -28,6 +29,10 @@ public class EngineImpl implements Engine {
     @Value("${my.engine.cylinders:6}") // <1>
     protected int cylinders;
 
+    @Nullable
+    @Value("${my.engine.description}")
+    protected String description;
+
     @Override
     public int getCylinders() {
         return cylinders;
@@ -38,5 +43,10 @@ public String start() {// <2>
         return "Starting V" + getCylinders() + " Engine";
     }
 
+    @Override
+    public String getDescription() {
+        return description;
+    }
+
 }
 // end::class[]

test-suite/src/test/java/io/micronaut/docs/config/value/VehicleSpec.java

@@ -24,6 +24,7 @@
 import java.util.LinkedHashMap;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
 
 class VehicleSpec {
 
@@ -56,4 +57,34 @@ void testStartVehicleWithoutConfiguration() {
         assertEquals("Starting V6 Engine", vehicle.start());
     }
 
+    @Test
+    void testStartVehicleWithNonEmptyPlaceholder() {
+        // tag::start[]
+        ApplicationContext applicationContext = new DefaultApplicationContext("test");
+        LinkedHashMap<String, Object> map = new LinkedHashMap(1);
+        map.put("my.engine.description", "${DESCRIPTION}");
+        map.put("DESCRIPTION", "V8 Engine");
+        applicationContext.getEnvironment().addPropertySource(PropertySource.of("test", map));
+        applicationContext.start();
+
+        Vehicle vehicle = applicationContext.getBean(Vehicle.class);
+        // end::start[]
+
+        assertEquals("V8 Engine", vehicle.getEngine().getDescription());
+    }
+
+    @Test
+    void testStartVehicleWithEmptyPlaceholder() {
+        // tag::start[]
+        ApplicationContext applicationContext = new DefaultApplicationContext("test");
+        LinkedHashMap<String, Object> map = new LinkedHashMap(1);
+        map.put("my.engine.description", "${DESCRIPTION}");
+        applicationContext.getEnvironment().addPropertySource(PropertySource.of("test", map));
+        applicationContext.start();
+
+        Vehicle vehicle = applicationContext.getBean(Vehicle.class);
+        // end::start[]
+
+        assertNull(vehicle.getEngine().getDescription());
+    }
 }