Add IBDO method to ensure data is available.

src/main/java/emissary/core/BaseDataObject.java

@@ -462,6 +462,16 @@ public void setData(@Nullable final byte[] newData, final int offset, final int
         safeUsageChecker.resetCacheThenRecordSnapshot(theData);
     }
 
+    /**
+     * Checks if the data is defined with a non-zero length.
+     * 
+     * @return if data is undefined or zero length.
+     */
+    @Override
+    public boolean isDataEmpty() throws IOException {
+        return getDataState() == DataState.NO_DATA || getChannelSize() == 0;
+    }
+
     /**
      * Convenience method to get the size of the channel or byte array providing access to the data.
      * 

src/main/java/emissary/core/IBaseDataObject.java

@@ -60,6 +60,13 @@ enum MergePolicy {
      */
     void setData(final byte[] newData, int offset, int length);
 
+    /**
+     * Checks if the data is defined with a non-zero length.
+     * 
+     * @return if data is undefined or zero length.
+     */
+    boolean isDataEmpty() throws IOException;
+
     /**
      * Set the byte channel factory using whichever implementation is providing access to the data.
      * 

src/test/java/emissary/core/BaseDataObjectTest.java

@@ -194,6 +194,17 @@ void testExceptionWhenGettingChannelSize() throws IOException {
         }
     }
 
+    @Test
+    void testIsDataEmpty() throws IOException {
+        final IBaseDataObject nullDataIbdo = new BaseDataObject();
+        final IBaseDataObject zeroLengthDataIbdo = new BaseDataObject(new byte[0], "zeroLengthDataIbdo");
+        final IBaseDataObject nonZeroLengthDataIbdo = new BaseDataObject(new byte[1], "nonZeroLengthDataIbdo");
+
+        assertTrue(nullDataIbdo.isDataEmpty());
+        assertTrue(zeroLengthDataIbdo.isDataEmpty());
+        assertFalse(nonZeroLengthDataIbdo.isDataEmpty());
+    }
+
     @Test
     void testDataLengthBothNull() {
         BaseDataObject bdo = new BaseDataObject();