Avoid setting p0 to None during assignment

[faridyagubbayli]

Fixed #468

Not sure why we even have a logic to assign p0 to None. Could not find any reason.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 73.16%. Comparing base (2dfa811) to head (364d9f7). Report is 34 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #543      +/-   ##
==========================================
+ Coverage   73.11%   73.16%   +0.04%     
==========================================
  Files          46       46              
  Lines        6830     6830              
  Branches     1308     1308              
==========================================
+ Hits         4994     4997       +3     
+ Misses       1286     1284       -2     
+ Partials      550      549       -1     

Flag	Coverage Δ
3.10	73.16% <100.00%> (+0.04%)	:arrow_up:
3.11	73.16% <100.00%> (+0.04%)	:arrow_up:
3.12	73.16% <100.00%> (+0.04%)	:arrow_up:
3.13	73.16% <100.00%> (+0.04%)	:arrow_up:
macos-latest	73.13% <100.00%> (+0.04%)	:arrow_up:
ubuntu-latest	73.13% <100.00%> (+0.04%)	:arrow_up:
windows-latest	73.14% <100.00%> (+0.04%)	:arrow_up:

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[waltsims]

import unittest
import numpy as np
from kwave.ksource import kSource

class TestKSource(unittest.TestCase):
    def setUp(self):
        self.source = kSource()

    def test_p0_setter_empty_array(self):
        """Test that p0 is set to None when given an empty array"""
        self.source.p0 = np.array([])
        self.assertIsNone(self.source.p0)

    def test_p0_setter_non_empty_array(self):
        """Test that p0 is set correctly for non-empty array"""
        test_array = np.array([1.0, 2.0, 3.0])
        self.source.p0 = test_array
        np.testing.assert_array_equal(self.source.p0, test_array)

    def test_p0_setter_zero_array(self):
        """Test that p0 is set correctly for array of zeros (should not be set to None)"""
        test_array = np.zeros(5)
        self.source.p0 = test_array
        np.testing.assert_array_equal(self.source.p0, test_array)

    def test_is_p0_empty(self):
        """Test the is_p0_empty method"""
        # Test with None
        self.assertTrue(self.source.is_p0_empty())
        
        # Test with empty array
        self.source.p0 = np.array([])
        self.assertTrue(self.source.is_p0_empty())
        
        # Test with non-empty array
        self.source.p0 = np.array([1.0, 2.0])
        self.assertFalse(self.source.is_p0_empty())
        
        # Test with zero array
        self.source.p0 = np.zeros(5)
        self.assertTrue(self.source.is_p0_empty())