diff --git a/b_asic/sfg_generators.py b/b_asic/sfg_generators.py
index 37d011f8bbeb593e3d7208671c93e547fd2a4562..68df38a400abf7a6876d0ecab0b7ffa3bdb82bf0 100644
--- a/b_asic/sfg_generators.py
+++ b/b_asic/sfg_generators.py
@@ -60,6 +60,8 @@ def wdf_allpass(
         Signal flow graph
     """
     np_coefficients = np.squeeze(np.asarray(coefficients))
+    if not np_coefficients:
+        raise ValueError("Coefficients cannot be empty")
     if np_coefficients.ndim != 1:
         raise TypeError("coefficients must be a 1D-array")
     if input_op is None:
@@ -120,12 +122,8 @@ def direct_form_fir(
     input_op: Optional[Union[Input, Signal, InputPort]] = None,
     output: Optional[Union[Output, Signal, OutputPort]] = None,
     name: Optional[str] = None,
-    mult_properties: Optional[
-        Union[Dict[str, int], Dict[str, Dict[str, int]]]
-    ] = None,
-    add_properties: Optional[
-        Union[Dict[str, int], Dict[str, Dict[str, int]]]
-    ] = None,
+    mult_properties: Optional[Union[Dict[str, int], Dict[str, Dict[str, int]]]] = None,
+    add_properties: Optional[Union[Dict[str, int], Dict[str, Dict[str, int]]]] = None,
 ):
     r"""
     Generate a signal flow graph of a direct form FIR filter. The *coefficients* parameter is a
@@ -166,6 +164,8 @@ def direct_form_fir(
     transposed_direct_form_fir
     """
     np_coefficients = np.squeeze(np.asarray(coefficients))
+    if not np_coefficients:
+        raise ValueError("Coefficients cannot be empty")
     if np_coefficients.ndim != 1:
         raise TypeError("coefficients must be a 1D-array")
     if input_op is None:
@@ -202,12 +202,8 @@ def transposed_direct_form_fir(
     input_op: Optional[Union[Input, Signal, InputPort]] = None,
     output: Optional[Union[Output, Signal, OutputPort]] = None,
     name: Optional[str] = None,
-    mult_properties: Optional[
-        Union[Dict[str, int], Dict[str, Dict[str, int]]]
-    ] = None,
-    add_properties: Optional[
-        Union[Dict[str, int], Dict[str, Dict[str, int]]]
-    ] = None,
+    mult_properties: Optional[Union[Dict[str, int], Dict[str, Dict[str, int]]]] = None,
+    add_properties: Optional[Union[Dict[str, int], Dict[str, Dict[str, int]]]] = None,
 ):
     r"""
     Generate a signal flow graph of a transposed direct form FIR filter. The *coefficients* parameter is a
@@ -248,6 +244,8 @@ def transposed_direct_form_fir(
     direct_form_fir
     """
     np_coefficients = np.squeeze(np.asarray(coefficients))
+    if not np_coefficients:
+        raise ValueError("Coefficients cannot be empty")
     if np_coefficients.ndim != 1:
         raise TypeError("coefficients must be a 1D-array")
     if input_op is None:
@@ -263,7 +261,6 @@ def transposed_direct_form_fir(
 
     taps = len(np_coefficients)
     prev_delay = None
-    prev_add = None
     for i, coeff in enumerate(reversed(np_coefficients)):
         tmp_mul = ConstantMultiplication(coeff, input_op, **mult_properties)
         tmp_add = (