Fix docs warnings

Author: justinabrahms

pom.xml

@@ -243,8 +243,18 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-javadoc-plugin</artifactId>
-        <version>2.9.1</version>
+        <version>3.4.0</version>
+        <configuration>
+          <failOnWarnings>true</failOnWarnings>
+        </configuration>
         <executions>
+          <execution>
+            <id>vet-javadoc</id>
+            <phase>validate</phase>
+            <goals>
+              <goal>jar</goal>
+            </goals>
+          </execution>
           <execution>
             <id>attach-javadocs</id>
             <goals>

src/main/java/dev/openfeature/javasdk/internal/ObjectUtils.java

@@ -11,6 +11,10 @@ public class ObjectUtils {
 
     /**
      * If the source param is null, return the default value.
+     * @param source maybe null object
+     * @param defaultValue thing to use if source is null
+     * @param <T> list type
+     * @return resulting object
      */
     public static <T> List<T> defaultIfNull(List<T> source, Supplier<List<T>> defaultValue) {
         if (source == null) {
@@ -21,6 +25,11 @@ public static <T> List<T> defaultIfNull(List<T> source, Supplier<List<T>> defaul
 
     /**
      * If the source param is null, return the default value.
+     * @param source maybe null object
+     * @param defaultValue thing to use if source is null
+     * @param <K> map key type
+     * @param <V> map value type
+     * @return resulting map
      */
     public static <K, V> Map<K, V> defaultIfNull(Map<K, V> source, Supplier<Map<K, V>> defaultValue) {
         if (source == null) {
@@ -31,6 +40,10 @@ public static <K, V> Map<K, V> defaultIfNull(Map<K, V> source, Supplier<Map<K, V
 
     /**
      * If the source param is null, return the default value.
+     * @param source maybe null object
+     * @param defaultValue thing to use if source is null
+     * @param <T> type
+     * @return resulting object
      */
     public static <T> T defaultIfNull(T source, Supplier<T> defaultValue) {
         if (source == null) {
@@ -41,6 +54,9 @@ public static <T> T defaultIfNull(T source, Supplier<T> defaultValue) {
 
     /**
      * Concatenate a bunch of lists.
+     * @param sources bunch of lists.
+     * @param <T> list type
+     * @return resulting object
      */
     @SafeVarargs
     public static <T> List<T> merge(List<T>... sources) {