Some improvements

.classpath

@@ -6,6 +6,12 @@
 			<attribute name="maven.pomderived" value="true"/>
 		</attributes>
 	</classpathentry>
+	<classpathentry kind="src" output="target/test-classes" path="src/test/java">
+		<attributes>
+			<attribute name="optional" value="true"/>
+			<attribute name="maven.pomderived" value="true"/>
+		</attributes>
+	</classpathentry>
 	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.7">
 		<attributes>
 			<attribute name="maven.pomderived" value="true"/>

pom.xml

@@ -28,16 +28,24 @@
 	</build>
 
 	<dependencies>
+
+	    <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.11</version>
+            <scope>test</scope>
+        </dependency>
+
 		<dependency>
 			<groupId>org.glassfish</groupId>
 			<artifactId>javax.json</artifactId>
 			<version>1.0-b02</version>
 		</dependency>
-		
-		<!-- <dependency> 
-		     <groupId>javax</groupId> 
-		     <artifactId>javaee-api</artifactId> 
-			 <version>7.0-b72</version> 
+
+		<!-- <dependency>
+		     <groupId>javax</groupId>
+		     <artifactId>javaee-api</artifactId>
+			 <version>7.0-b72</version>
 	    </dependency> -->
 	</dependencies>
 </project>

src/main/java/JSR353/JSON/PricesCacheStore.java

@@ -2,37 +2,37 @@
 
 import java.util.concurrent.ConcurrentHashMap;
 
-public class PricesCacheStore {
+public enum PricesCacheStore {
+
+	INSTANCE;
 
-	private final static PricesCacheStore INSTANCE = new PricesCacheStore();	
-
-	private PricesCacheStore() {}
 	private volatile String lastSymboleUpdated;
-
-	// will contain Symbols and prices stored and constantly updated	
-	private volatile ConcurrentHashMap<String, Double> pricesCache = new ConcurrentHashMap<>(); 
-
-	public static PricesCacheStore getInstance() {
-		return INSTANCE; 
-	}
-
+
+	// will contain Symbols and prices stored and constantly updated
+	private volatile ConcurrentHashMap<String, Double> pricesCache = new ConcurrentHashMap<>();
+
 	public void addPrice(String symbol, Double price) {
-		pricesCache.put(symbol, price);
-		lastSymboleUpdated = symbol; 
+		if (symbol != null && price != null) {
+		    pricesCache.put(symbol, price);
+		    lastSymboleUpdated = symbol;
+		}
 	}
-	
+
 	public Double getPrice(String symbol) {
+		if (symbol == null) {
+			return 0d;
+		}
 		Double price = pricesCache.get(symbol);
-		return price == null ? 0 : price;
+		return price == null ? 0d : price;
 	}
-	
+
 	// Keep in mind immutability - return a copy of the object
 	// does not matter if it is static or volatile
 	// or if its threading is safe
-	public ConcurrentHashMap<String, Double> getAllPrices() {		
+	public ConcurrentHashMap<String, Double> getAllPrices() {
 		return new ConcurrentHashMap<String, Double>(pricesCache);
 	}
-	
+
 	public String getLastSymbolUpdated() {
 		return new String(lastSymboleUpdated);
 	}