Ignore empty prefixes in new PrefixedConfigurationPropertySource

See gh-25445

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/PrefixedConfigurationPropertySource.java

@@ -47,7 +47,10 @@ class PrefixedConfigurationPropertySource implements ConfigurationPropertySource
 	}
 
 	private ConfigurationPropertyName getPrefixedName(ConfigurationPropertyName name) {
-		String prefix = (StringUtils.hasText(this.prefix)) ? this.prefix + "." : "";
+		if (!StringUtils.hasText(this.prefix)) {
+			return name;
+		}
+		String prefix = this.prefix + ".";
 		return ConfigurationPropertyName.of(prefix + name);
 	}
 

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/PrefixedIterableConfigurationPropertySource.java

@@ -18,6 +18,8 @@ package org.springframework.boot.context.properties.source;
 
 import java.util.stream.Stream;
 
+import org.springframework.util.StringUtils;
+
 /**
  * An iterable {@link PrefixedConfigurationPropertySource}.
  *
@@ -32,6 +34,9 @@ class PrefixedIterableConfigurationPropertySource extends PrefixedConfigurationP
 
 	@Override
 	public Stream<ConfigurationPropertyName> stream() {
+		if (!StringUtils.hasText(getPrefix())) {
+			return getSource().stream();
+		}
 		ConfigurationPropertyName prefix = ConfigurationPropertyName.of(getPrefix());
 		return getSource().stream().map((propertyName) -> {
 			if (prefix.isAncestorOf(propertyName)) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/PrefixedIterableConfigurationPropertySourceTests.java

@@ -38,4 +38,15 @@ class PrefixedIterableConfigurationPropertySourceTests {
 				ConfigurationPropertyName.of("foo.baz"), ConfigurationPropertyName.of("hello.bing"));
 	}
 
+	@Test
+	void emptyPrefixShouldReturnOriginalStream() {
+		MockConfigurationPropertySource source = new MockConfigurationPropertySource();
+		source.put("my.foo.bar", "bing");
+		source.put("my.foo.baz", "biff");
+		source.put("hello.bing", "blah");
+		IterableConfigurationPropertySource prefixed = source.withPrefix("");
+		assertThat(prefixed.stream()).containsExactly(ConfigurationPropertyName.of("my.foo.bar"),
+				ConfigurationPropertyName.of("my.foo.baz"), ConfigurationPropertyName.of("hello.bing"));
+	}
+
 }