Added null check to EMAFilter

src/main/java/com/thealgorithms/audiofilters/EMAFilter.java

@@ -3,16 +3,19 @@
 /**
  * Exponential Moving Average (EMA) Filter for smoothing audio signals.
  *
- * <p>This filter applies an exponential moving average to a sequence of audio
+ * <p>
+ * This filter applies an exponential moving average to a sequence of audio
  * signal values, making it useful for smoothing out rapid fluctuations.
  * The smoothing factor (alpha) controls the degree of smoothing.
  *
- * <p>Based on the definition from
+ * <p>
+ * Based on the definition from
  * <a href="https://en.wikipedia.org/wiki/Moving_average">Wikipedia link</a>.
  */
 public class EMAFilter {
     private final double alpha;
     private double emaValue;
+
     /**
      * Constructs an EMA filter with a given smoothing factor.
      *
@@ -26,14 +29,17 @@ public EMAFilter(double alpha) {
         this.alpha = alpha;
         this.emaValue = 0.0;
     }
+
     /**
      * Applies the EMA filter to an audio signal array.
+     * EMA formula:
+     * EMA = alpha * currentSample + (1 - alpha) * previousEMA
      *
      * @param audioSignal Array of audio samples to process
      * @return Array of processed (smoothed) samples
      */
     public double[] apply(double[] audioSignal) {
-        if (audioSignal.length == 0) {
+        if (audioSignal == null || audioSignal.length == 0) {
             return new double[0];
         }
         double[] emaSignal = new double[audioSignal.length];