BigFraction: Document exception thrown by reciprocal when zero.
diff --git a/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/BigFraction.java b/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/BigFraction.java
index d0411f0..541fb6c 100644
--- a/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/BigFraction.java
+++ b/commons-numbers-fraction/src/main/java/org/apache/commons/numbers/fraction/BigFraction.java
@@ -521,6 +521,13 @@
         return new BigFraction(numerator.negate(), denominator);
     }
 
+    /**
+     * {@inheritDoc}
+     *
+     * <p>Raises an exception if the fraction is equal to zero.
+     *
+     * @throws ArithmeticException if the current numerator is {@code zero}
+     */
     @Override
     public BigFraction reciprocal() {
         return new BigFraction(denominator, numerator);