Update TextLoader.cs

Author: mstfbl

src/Microsoft.ML.Data/DataLoadSave/Text/TextLoader.cs

@@ -479,7 +479,10 @@ public class Options
 
             /// <summary>
             /// Whether the data file has a header with feature names.
-            /// Note: If a TextLoader is created with HasHeader=true but without a dataSample, then the TextLoader will not contain slot (columns that are chosen for manipulation) names, because the output schema is made when the TextLoader is made, and not when TextLoader.Load(IMultiStreamSource source) is called.
+            /// Note: If a TextLoader is created with HasHeader = true but without a dataSample, then vector columns made by TextLoader will not contain slot name
+            /// annotations (slots being the elements of the given vector column), because the output schema is made when the TextLoader is made, and not when
+            /// TextLoader.Load(IMultiStreamSource source) is called. In addition, the case where dataSample = null and HasHeader = true indicates to the
+            /// loader that when it is given a file when Load is called, it needs to skip the first line.
             /// </summary>
             [Argument(ArgumentType.AtMostOnce, ShortName = "header",
                 HelpText = "Data file has header with feature names. Header is read only if options 'hs' and 'hf' are not specified.")]
@@ -680,9 +683,6 @@ public Bindings(TextLoader parent, Column[] cols, IMultiStreamSource headerFile,
                             needInputSize = true;
                     }
 
-                    if (parent.HasHeader && dataSample == null)
-                        throw ch.ExceptNotSupp("Data sample cannot be null if the HasHeader flag is set to True.");
-
                     int inputSize = parent._inputSize;
                     ch.Assert(0 <= inputSize & inputSize < SrcLim);
                     List<ReadOnlyMemory<char>> lines = null;