diff --git a/acro/acro_stata_parser.py b/acro/acro_stata_parser.py
index b9e5cbc..d263413 100644
--- a/acro/acro_stata_parser.py
+++ b/acro/acro_stata_parser.py
@@ -138,6 +138,7 @@ def parse_table_details(
     >> table rowvar [colvar [supercolvar] [if] [in] [weight] [, options].
     """
     details: dict = {"errmsg": "", "rowvars": list([]), "colvars": list([])}
+    contents_found, content = False, []
 
     if stata_version == "16":
         details["rowvars"] = [varlist.pop(0)]
@@ -326,6 +327,7 @@ def extract_var_within_parentheses(input_string):
     """Given a string, this function extracts the words within the first parentheses
     from a string.
     """
+    string = ""
     string_match = re.match(r"\((.*?)\)", input_string)
     if string_match:
         string = string_match.group(1).strip()
@@ -335,6 +337,7 @@ def extract_var_within_parentheses(input_string):
 
 def extract_var_before_parentheses(input_string):
     """Given a string, this function extracts the words before the first parentheses."""
+    string = ""
     string_match = re.match(r"^(.*?)\(", input_string)
     if string_match:
         string = string_match.group(1).strip()
@@ -346,6 +349,7 @@ def extract_table_var(input_string):
     """Given a string, this function extracts the words within the parentheses.
     If there are no parentheses the string is returned.
     """
+    string = ""
     # If the string starts with parentheses
     if input_string.startswith("("):
         string, _ = extract_var_within_parentheses(input_string)
diff --git a/acro/acro_tables.py b/acro/acro_tables.py
index c78c451..3c97a5e 100644
--- a/acro/acro_tables.py
+++ b/acro/acro_tables.py
@@ -555,13 +555,13 @@ def hist(  # pylint: disable=too-many-arguments,too-many-locals
         self,
         data,
         column,
-        by=None,
+        by_val=None,
         grid=True,
         xlabelsize=None,
         xrot=None,
         ylabelsize=None,
         yrot=None,
-        ax=None,
+        axis=None,
         sharex=False,
         sharey=False,
         figsize=None,
@@ -586,7 +586,7 @@ def hist(  # pylint: disable=too-many-arguments,too-many-locals
             The pandas object holding the data.
         column : str
             The column that will be used to plot the histogram.
-        by : object, optional
+        by_val : object, optional
             If passed, then used to form histograms for separate groups.
         grid : bool, default True
             Whether to show axis grid lines.
@@ -600,7 +600,7 @@ def hist(  # pylint: disable=too-many-arguments,too-many-locals
         yrot : float, default None
             Rotation of y axis labels. For example, a value of 90 displays
             the y labels rotated 90 degrees clockwise.
-        ax : Matplotlib axes object, default None
+        axis : Matplotlib axes object, default None
             The axes to plot the histogram on.
         sharex : bool, default True if ax is None else False
             In case subplots=True, share x axis and set some x axis labels to invisible;
@@ -662,13 +662,13 @@ def hist(  # pylint: disable=too-many-arguments,too-many-locals
             else:  # pragma: no cover
                 data.hist(
                     column=column,
-                    by=by,
+                    by=by_val,
                     grid=grid,
                     xlabelsize=xlabelsize,
                     xrot=xrot,
                     ylabelsize=ylabelsize,
                     yrot=yrot,
-                    ax=ax,
+                    ax=axis,
                     sharex=sharex,
                     sharey=sharey,
                     figsize=figsize,
@@ -682,13 +682,13 @@ def hist(  # pylint: disable=too-many-arguments,too-many-locals
             status = "review"
             data.hist(
                 column=column,
-                by=by,
+                by=by_val,
                 grid=grid,
                 xlabelsize=xlabelsize,
                 xrot=xrot,
                 ylabelsize=ylabelsize,
                 yrot=yrot,
-                ax=ax,
+                ax=axis,
                 sharex=sharex,
                 sharey=sharey,
                 figsize=figsize,
@@ -1364,15 +1364,31 @@ def create_dataframe(index, columns) -> DataFrame:
     Dataframe
         Table of the index and columns combined.
     """
-    if isinstance(index, list):
-        index_df = pd.concat(index, axis=1)
-    elif isinstance(index, pd.Series):
-        index_df = pd.DataFrame({index.name: index})
-    if isinstance(columns, list):
-        columns_df = pd.concat(columns, axis=1)
-    elif isinstance(columns, pd.Series):
-        columns_df = pd.DataFrame({columns.name: columns})
-    data = pd.concat([index_df, columns_df], axis=1)
+    empty_dataframe = pd.DataFrame([])
+
+    index_df = empty_dataframe
+    try:
+        if isinstance(index, list):
+            index_df = pd.concat(index, axis=1)
+        elif isinstance(index, pd.Series):
+            index_df = pd.DataFrame({index.name: index})
+    except ValueError:
+        index_df = empty_dataframe
+
+    columns_df = empty_dataframe
+    try:
+        if isinstance(columns, list):
+            columns_df = pd.concat(columns, axis=1)
+        elif isinstance(columns, pd.Series):
+            columns_df = pd.DataFrame({columns.name: columns})
+    except ValueError:
+        columns_df = empty_dataframe
+
+    try:
+        data = pd.concat([index_df, columns_df], axis=1)
+    except ValueError:
+        data = empty_dataframe
+
     return data