Provide ability to filter dataframe column by null via ElementWise Methods

src/Microsoft.Data.Analysis/DataFrameColumn.BinaryOperations.cs

@@ -316,5 +316,20 @@ public virtual PrimitiveDataFrameColumn<bool> ElementwiseLessThan<T>(T value)
             throw new NotImplementedException();
         }
 
+        /// <summary>
+        /// Performs an element-wise equal to Null on each value in the column
+        /// </summary>
+        public virtual PrimitiveDataFrameColumn<bool> ElementwiseIsNull()
+        {
+            throw new NotImplementedException();
+        }
+
+        /// <summary>
+        /// Performs an element-wise not equal to Null on each value in the column
+        /// </summary>
+        public virtual PrimitiveDataFrameColumn<bool> ElementwiseIsNotNull()
+        {
+            throw new NotImplementedException();
+        }
     }
 }

src/Microsoft.Data.Analysis/DataFrameColumn.BinaryOperations.tt

@@ -78,5 +78,14 @@ namespace Microsoft.Data.Analysis
 
 <# } #>
 <# } #>
+        public virtual PrimitiveDataFrameColumn<bool> ElementwiseIsNull()
+        {
+            throw new NotImplementedException();
+        }
+
+        public virtual PrimitiveDataFrameColumn<bool> ElementwiseIsNotNull()
+        {
+            throw new NotImplementedException();
+        }
     }
 }